diff --git a/eth2/lmd_ghost/src/reduced_tree.rs b/eth2/lmd_ghost/src/reduced_tree.rs
deleted file mode 100644
index d0798afd20..0000000000
--- a/eth2/lmd_ghost/src/reduced_tree.rs
+++ /dev/null
@@ -1,1027 +0,0 @@
-//! An implementation of "reduced tree" LMD GHOST fork choice.
-//!
-//! This algorithm was conceived at IC3 Cornell, 2019.
-//!
-//! This implementation is incomplete and has known bugs. Do not use in production.
-use super::{LmdGhost, Result as SuperResult};
-use itertools::Itertools;
-use parking_lot::RwLock;
-use ssz::{Decode, Encode};
-use ssz_derive::{Decode, Encode};
-use std::cmp::Ordering;
-use std::collections::HashMap;
-use std::fmt;
-use std::marker::PhantomData;
-use std::sync::Arc;
-use store::{BlockRootTree, Error as StoreError, Store};
-use types::{BeaconBlock, EthSpec, Hash256, Slot};
-
-type Result<T> = std::result::Result<T, Error>;
-
-#[derive(Debug, PartialEq)]
-pub enum Error {
-    MissingNode(Hash256),
-    MissingBlock(Hash256),
-    MissingState(Hash256),
-    MissingChild(Hash256),
-    MissingSuccessor(Hash256, Hash256),
-    NotInTree(Hash256),
-    NoCommonAncestor((Hash256, Hash256)),
-    StoreError(StoreError),
-    ValidatorWeightUnknown(usize),
-    SszDecodingError(ssz::DecodeError),
-    InvalidReducedTreeSsz(String),
-}
-
-impl From<StoreError> for Error {
-    fn from(e: StoreError) -> Error {
-        Error::StoreError(e)
-    }
-}
-
-impl From<ssz::DecodeError> for Error {
-    fn from(e: ssz::DecodeError) -> Error {
-        Error::SszDecodingError(e)
-    }
-}
-
-pub struct ThreadSafeReducedTree<T, E> {
-    core: RwLock<ReducedTree<T, E>>,
-}
-
-impl<T, E> fmt::Debug for ThreadSafeReducedTree<T, E> {
-    /// `Debug` just defers to the implementation of `self.core`.
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.core.fmt(f)
-    }
-}
-
-impl<T, E> PartialEq for ThreadSafeReducedTree<T, E> {
-    /// This implementation ignores the `store`.
-    fn eq(&self, other: &Self) -> bool {
-        *self.core.read() == *other.core.read()
-    }
-}
-
-impl<T, E> LmdGhost<T, E> for ThreadSafeReducedTree<T, E>
-where
-    T: Store<E>,
-    E: EthSpec,
-{
-    fn new(
-        store: Arc<T>,
-        block_root_tree: Arc<BlockRootTree>,
-        genesis_block: &BeaconBlock<E>,
-        genesis_root: Hash256,
-    ) -> Self {
-        ThreadSafeReducedTree {
-            core: RwLock::new(ReducedTree::new(
-                store,
-                block_root_tree,
-                genesis_block,
-                genesis_root,
-            )),
-        }
-    }
-
-    fn process_attestation(
-        &self,
-        validator_index: usize,
-        block_hash: Hash256,
-        block_slot: Slot,
-    ) -> SuperResult<()> {
-        self.core
-            .write()
-            .process_message(validator_index, block_hash, block_slot)
-            .map_err(|e| format!("process_attestation failed: {:?}", e))
-    }
-
-    /// Process a block that was seen on the network.
-    fn process_block(&self, block: &BeaconBlock<E>, block_hash: Hash256) -> SuperResult<()> {
-        self.core
-            .write()
-            .maybe_add_weightless_node(block.slot, block_hash)
-            .map_err(|e| format!("process_block failed: {:?}", e))
-    }
-
-    fn find_head<F>(
-        &self,
-        start_block_slot: Slot,
-        start_block_root: Hash256,
-        weight_fn: F,
-    ) -> SuperResult<Hash256>
-    where
-        F: Fn(usize) -> Option<u64> + Copy,
-    {
-        self.core
-            .write()
-            .update_weights_and_find_head(start_block_slot, start_block_root, weight_fn)
-            .map_err(|e| format!("find_head failed: {:?}", e))
-    }
-
-    fn update_finalized_root(
-        &self,
-        new_block: &BeaconBlock<E>,
-        new_root: Hash256,
-    ) -> SuperResult<()> {
-        self.core
-            .write()
-            .update_root(new_block.slot, new_root)
-            .map_err(|e| format!("update_finalized_root failed: {:?}", e))
-    }
-
-    fn latest_message(&self, validator_index: usize) -> Option<(Hash256, Slot)> {
-        self.core.read().latest_message(validator_index)
-    }
-
-    fn verify_integrity(&self) -> SuperResult<()> {
-        self.core.read().verify_integrity()
-    }
-
-    /// Consume the `ReducedTree` object and return its ssz encoded bytes representation.
-    fn as_bytes(&self) -> Vec<u8> {
-        self.core.read().as_bytes()
-    }
-
-    /// Create a new `ThreadSafeReducedTree` instance from a `store` and the
-    /// encoded ssz bytes representation.
-    ///
-    /// Returns an error if ssz bytes are not a valid `ReducedTreeSsz` object.
-    fn from_bytes(
-        bytes: &[u8],
-        store: Arc<T>,
-        block_root_tree: Arc<BlockRootTree>,
-    ) -> SuperResult<Self> {
-        Ok(ThreadSafeReducedTree {
-            core: RwLock::new(
-                ReducedTree::from_bytes(bytes, store, block_root_tree)
-                    .map_err(|e| format!("Cannot decode ssz bytes {:?}", e))?,
-            ),
-        })
-    }
-}
-
-/// Intermediate representation of a `ReducedTree` `LmdGhost` fork choice.
-#[derive(Debug, PartialEq, Encode, Decode)]
-struct ReducedTreeSsz {
-    pub node_hashes: Vec<Hash256>,
-    pub nodes: Vec<Node>,
-    pub latest_votes: Vec<Option<Vote>>,
-    pub root_hash: Hash256,
-    pub root_slot: Slot,
-}
-
-impl ReducedTreeSsz {
-    pub fn from_reduced_tree<T, E>(tree: &ReducedTree<T, E>) -> Self {
-        let (node_hashes, nodes): (Vec<_>, Vec<_>) = tree.nodes.clone().into_iter().unzip();
-        ReducedTreeSsz {
-            node_hashes,
-            nodes,
-            latest_votes: tree.latest_votes.0.clone(),
-            root_hash: tree.root.0,
-            root_slot: tree.root.1,
-        }
-    }
-
-    pub fn into_reduced_tree<T, E>(
-        self,
-        store: Arc<T>,
-        block_root_tree: Arc<BlockRootTree>,
-    ) -> Result<ReducedTree<T, E>> {
-        if self.node_hashes.len() != self.nodes.len() {
-            return Err(Error::InvalidReducedTreeSsz(
-                "node_hashes and nodes should have equal length".to_string(),
-            ));
-        }
-        let nodes: HashMap<_, _> = self
-            .node_hashes
-            .into_iter()
-            .zip(self.nodes.into_iter())
-            .collect();
-        let latest_votes = ElasticList(self.latest_votes);
-        let root = (self.root_hash, self.root_slot);
-        Ok(ReducedTree {
-            store,
-            block_root_tree,
-            nodes,
-            latest_votes,
-            root,
-            _phantom: PhantomData,
-        })
-    }
-}
-
-#[derive(Clone)]
-struct ReducedTree<T, E> {
-    store: Arc<T>,
-    block_root_tree: Arc<BlockRootTree>,
-    /// Stores all nodes of the tree, keyed by the block hash contained in the node.
-    nodes: HashMap<Hash256, Node>,
-    /// Maps validator indices to their latest votes.
-    latest_votes: ElasticList<Option<Vote>>,
-    /// Stores the root of the tree, used for pruning.
-    root: (Hash256, Slot),
-    _phantom: PhantomData<E>,
-}
-
-impl<T, E> fmt::Debug for ReducedTree<T, E> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.nodes.fmt(f)
-    }
-}
-
-impl<T, E> PartialEq for ReducedTree<T, E> {
-    /// This implementation ignores the `store` field.
-    fn eq(&self, other: &Self) -> bool {
-        self.nodes == other.nodes
-            && self.latest_votes == other.latest_votes
-            && self.root == other.root
-    }
-}
-
-impl<T, E> ReducedTree<T, E>
-where
-    T: Store<E>,
-    E: EthSpec,
-{
-    pub fn new(
-        store: Arc<T>,
-        block_root_tree: Arc<BlockRootTree>,
-        genesis_block: &BeaconBlock<E>,
-        genesis_root: Hash256,
-    ) -> Self {
-        let mut nodes = HashMap::new();
-
-        // Insert the genesis node.
-        nodes.insert(genesis_root, Node::new(genesis_root));
-
-        Self {
-            store,
-            block_root_tree,
-            nodes,
-            latest_votes: ElasticList::default(),
-            root: (genesis_root, genesis_block.slot),
-            _phantom: PhantomData,
-        }
-    }
-
-    /// Set the root node (the node without any parents) to the given `new_slot` and `new_root`.
-    ///
-    /// The given `new_root` must be in the block tree (but not necessarily in the reduced tree).
-    /// Any nodes which are not a descendant of `new_root` will be removed from the store.
-    pub fn update_root(&mut self, new_slot: Slot, new_root: Hash256) -> Result<()> {
-        self.maybe_add_weightless_node(new_slot, new_root)?;
-
-        self.retain_subtree(self.root.0, new_root)?;
-
-        self.root = (new_root, new_slot);
-
-        let root_node = self.get_mut_node(new_root)?;
-        root_node.parent_hash = None;
-
-        Ok(())
-    }
-
-    /// Removes `current_hash` and all descendants, except `subtree_hash` and all nodes
-    /// which have `subtree_hash` as an ancestor.
-    ///
-    /// In effect, prunes the tree so that only decendants of `subtree_hash` exist.
-    fn retain_subtree(&mut self, current_hash: Hash256, subtree_hash: Hash256) -> Result<()> {
-        if current_hash != subtree_hash {
-            let children = self.get_node(current_hash)?.children.clone();
-
-            for child in children {
-                self.retain_subtree(child.hash, subtree_hash)?;
-            }
-
-            self.nodes.remove(&current_hash);
-        }
-
-        Ok(())
-    }
-
-    pub fn process_message(
-        &mut self,
-        validator_index: usize,
-        block_hash: Hash256,
-        slot: Slot,
-    ) -> Result<()> {
-        if slot >= self.root_slot() {
-            if let Some(previous_vote) = self.latest_votes.get(validator_index) {
-                // Note: it is possible to do a cheap equivocation check here:
-                //
-                // slashable = (previous_vote.slot == slot) && (previous_vote.hash != block_hash)
-
-                if previous_vote.slot < slot {
-                    self.remove_latest_message(validator_index)?;
-                } else {
-                    return Ok(());
-                }
-            }
-
-            self.latest_votes.insert(
-                validator_index,
-                Some(Vote {
-                    slot,
-                    hash: block_hash,
-                }),
-            );
-
-            self.add_latest_message(validator_index, block_hash)?;
-        }
-
-        Ok(())
-    }
-
-    pub fn update_weights_and_find_head<F>(
-        &mut self,
-        start_block_slot: Slot,
-        start_block_root: Hash256,
-        weight_fn: F,
-    ) -> Result<Hash256>
-    where
-        F: Fn(usize) -> Option<u64> + Copy,
-    {
-        // It is possible that the given `start_block_root` is not in the reduced tree.
-        //
-        // In this case, we add a weightless node at `start_block_root`.
-        if !self.nodes.contains_key(&start_block_root) {
-            self.maybe_add_weightless_node(start_block_slot, start_block_root)?;
-        };
-
-        let _root_weight = self.update_weight(start_block_root, weight_fn)?;
-
-        let start_node = self.get_node(start_block_root)?;
-        let head_node = self.find_head_from(start_node, start_block_slot)?;
-
-        Ok(head_node.block_hash)
-    }
-
-    pub fn latest_message(&self, validator_index: usize) -> Option<(Hash256, Slot)> {
-        match self.latest_votes.get_ref(validator_index) {
-            Some(Some(v)) => Some((v.hash, v.slot)),
-            _ => None,
-        }
-    }
-
-    // Corresponds to the loop in `get_head` in the spec.
-    fn find_head_from<'a>(
-        &'a self,
-        start_node: &'a Node,
-        justified_slot: Slot,
-    ) -> Result<&'a Node> {
-        let children = start_node
-            .children
-            .iter()
-            // This check is primarily for the first iteration, where we must ensure that
-            // we only consider votes that were made after the last justified checkpoint.
-            .filter(|c| c.successor_slot > justified_slot)
-            .map(|c| self.get_node(c.hash))
-            .collect::<Result<Vec<&Node>>>()?;
-
-        if children.is_empty() {
-            Ok(start_node)
-        } else {
-            let best_child = children
-                .iter()
-                .max_by_key(|child| (child.weight, child.block_hash))
-                // There can only be no maximum if there are no children. This code path is guarded
-                // against that condition.
-                .expect("There must be a maximally weighted node.");
-
-            self.find_head_from(best_child, justified_slot)
-        }
-    }
-
-    fn update_weight<F>(&mut self, start_block_root: Hash256, weight_fn: F) -> Result<u64>
-    where
-        F: Fn(usize) -> Option<u64> + Copy,
-    {
-        let weight = {
-            let node = self.get_node(start_block_root)?.clone();
-
-            let mut weight = 0;
-
-            for child in &node.children {
-                weight += self.update_weight(child.hash, weight_fn)?;
-            }
-
-            for &voter in &node.voters {
-                weight += weight_fn(voter).ok_or_else(|| Error::ValidatorWeightUnknown(voter))?;
-            }
-
-            weight
-        };
-
-        let node = self.get_mut_node(start_block_root)?;
-        node.weight = weight;
-
-        Ok(weight)
-    }
-
-    /// Removes the vote from `validator_index` from the reduced tree.
-    ///
-    /// If the validator had a vote in the tree, the removal of that vote may cause a node to
-    /// become redundant and removed from the reduced tree.
-    fn remove_latest_message(&mut self, validator_index: usize) -> Result<()> {
-        if let Some(vote) = *self.latest_votes.get(validator_index) {
-            if self.nodes.contains_key(&vote.hash) {
-                self.get_mut_node(vote.hash)?.remove_voter(validator_index);
-                let node = self.get_node(vote.hash)?.clone();
-
-                if let Some(parent_hash) = node.parent_hash {
-                    if node.has_votes() || node.children.len() > 1 {
-                        // A node with votes or more than one child is never removed.
-                    } else if node.children.len() == 1 {
-                        // A node which has only one child may be removed.
-                        //
-                        // Load the child of the node and set it's parent to be the parent of this
-                        // node (viz., graft the node's child to the node's parent)
-                        let child = self.get_mut_node(node.children[0].hash)?;
-                        child.parent_hash = node.parent_hash;
-
-                        // Graft the parent of this node to it's child.
-                        if let Some(parent_hash) = node.parent_hash {
-                            let parent = self.get_mut_node(parent_hash)?;
-                            parent.replace_child_hash(node.block_hash, node.children[0].hash)?;
-                        }
-
-                        self.nodes.remove(&vote.hash);
-                    } else if node.children.is_empty() {
-                        // Remove the to-be-deleted node from it's parent.
-                        if let Some(parent_hash) = node.parent_hash {
-                            self.get_mut_node(parent_hash)?
-                                .remove_child(node.block_hash)?;
-                        }
-
-                        self.nodes.remove(&vote.hash);
-
-                        // A node which has no children may be deleted and potentially it's parent
-                        // too.
-                        self.maybe_delete_node(parent_hash)?;
-                    } else {
-                        // It is impossible for a node to have a number of children that is not 0, 1 or
-                        // greater than one.
-                        //
-                        // This code is strictly unnecessary, however we keep it for readability.
-                        unreachable!();
-                    }
-                } else {
-                    // A node without a parent is the genesis/finalized node and should never be removed.
-                }
-
-                self.latest_votes.insert(validator_index, Some(vote));
-            }
-        }
-
-        Ok(())
-    }
-
-    /// Deletes a node if it is unnecessary.
-    ///
-    /// Any node is unnecessary if all of the following are true:
-    ///
-    /// - it is not the root node.
-    /// - it only has one child.
-    /// - it does not have any votes.
-    fn maybe_delete_node(&mut self, hash: Hash256) -> Result<()> {
-        let should_delete = {
-            if let Ok(node) = self.get_node(hash) {
-                let node = node.clone();
-
-                if let Some(parent_hash) = node.parent_hash {
-                    if node.children.len() == 1 && !node.has_votes() {
-                        let child = &node.children[0];
-
-                        // Graft the single descendant `node` to the `parent` of node.
-                        self.get_mut_node(child.hash)?.parent_hash = Some(parent_hash);
-
-                        // Detach `node` from `parent`, replacing it with `child`.
-                        // Preserve the parent's direct descendant slot.
-                        self.get_mut_node(parent_hash)?
-                            .replace_child_hash(hash, child.hash)?;
-
-                        true
-                    } else {
-                        false
-                    }
-                } else {
-                    // A node without a parent is the genesis node and should not be deleted.
-                    false
-                }
-            } else {
-                // No need to delete a node that does not exist.
-                false
-            }
-        };
-
-        if should_delete {
-            self.nodes.remove(&hash);
-        }
-
-        Ok(())
-    }
-
-    fn add_latest_message(&mut self, validator_index: usize, hash: Hash256) -> Result<()> {
-        if let Ok(node) = self.get_mut_node(hash) {
-            node.add_voter(validator_index);
-        } else {
-            let node = Node {
-                voters: vec![validator_index],
-                ..Node::new(hash)
-            };
-
-            self.add_node(node)?;
-        }
-
-        Ok(())
-    }
-
-    fn maybe_add_weightless_node(&mut self, slot: Slot, hash: Hash256) -> Result<()> {
-        if slot > self.root_slot() && !self.nodes.contains_key(&hash) {
-            let node = Node::new(hash);
-
-            self.add_node(node)?;
-
-            // Read the `parent_hash` from the newly created node. If it has a parent (i.e., it's
-            // not the root), see if it is superfluous.
-            if let Some(parent_hash) = self.get_node(hash)?.parent_hash {
-                self.maybe_delete_node(parent_hash)?;
-            }
-        }
-
-        Ok(())
-    }
-
-    /// Find the direct successor block of `ancestor` if `descendant` is a descendant.
-    fn find_ancestor_successor_opt(
-        &self,
-        ancestor: Hash256,
-        descendant: Hash256,
-    ) -> Result<Option<Hash256>> {
-        Ok(self
-            .iter_ancestors(descendant, true)
-            .take_while(|(_, slot)| *slot >= self.root_slot())
-            .map(|(block_hash, _)| block_hash)
-            .tuple_windows()
-            .find_map(|(successor, block_hash)| {
-                if block_hash == ancestor {
-                    Some(successor)
-                } else {
-                    None
-                }
-            }))
-    }
-
-    /// Same as `find_ancestor_successor_opt` but will return an error instead of an option.
-    fn find_ancestor_successor(&self, ancestor: Hash256, descendant: Hash256) -> Result<Hash256> {
-        self.find_ancestor_successor_opt(ancestor, descendant)?
-            .ok_or_else(|| Error::MissingSuccessor(ancestor, descendant))
-    }
-
-    /// Look up the successor of the given `ancestor`, returning the slot of that block.
-    fn find_ancestor_successor_slot(&self, ancestor: Hash256, descendant: Hash256) -> Result<Slot> {
-        let successor_hash = self.find_ancestor_successor(ancestor, descendant)?;
-        Ok(self.get_block(successor_hash)?.slot)
-    }
-
-    /// Add `node` to the reduced tree, returning an error if `node` is not rooted in the tree.
-    fn add_node(&mut self, mut node: Node) -> Result<()> {
-        // Find the highest (by slot) ancestor of the given node in the reduced tree.
-        //
-        // If this node has no ancestor in the tree, exit early.
-        let mut prev_in_tree = self
-            .find_prev_in_tree(&node)
-            .ok_or_else(|| Error::NotInTree(node.block_hash))
-            .and_then(|hash| self.get_node(hash))?
-            .clone();
-
-        // If the ancestor of `node` has children, there are three possible operations:
-        //
-        // 1. Graft the `node` between two existing nodes.
-        // 2. Create another node that will be grafted between two existing nodes, then graft
-        //    `node` to it.
-        // 3. Graft `node` to an existing node.
-        if !prev_in_tree.children.is_empty() {
-            for child_link in &prev_in_tree.children {
-                let child_hash = child_link.hash;
-
-                // 1. Graft the new node between two existing nodes.
-                //
-                // If `node` is a descendant of `prev_in_tree` but an ancestor of a child connected to
-                // `prev_in_tree`.
-                //
-                // This means that `node` can be grafted between `prev_in_tree` and the child that is a
-                // descendant of both `node` and `prev_in_tree`.
-                if let Some(successor) =
-                    self.find_ancestor_successor_opt(node.block_hash, child_hash)?
-                {
-                    let successor_slot = self.get_block(successor)?.slot;
-                    let child = self.get_mut_node(child_hash)?;
-
-                    // Graft `child` to `node`.
-                    child.parent_hash = Some(node.block_hash);
-                    // Graft `node` to `child`.
-                    node.children.push(ChildLink {
-                        hash: child_hash,
-                        successor_slot,
-                    });
-                    // Detach `child` from `prev_in_tree`, replacing it with `node`.
-                    prev_in_tree.replace_child_hash(child_hash, node.block_hash)?;
-                    // Graft `node` to `prev_in_tree`.
-                    node.parent_hash = Some(prev_in_tree.block_hash);
-
-                    break;
-                }
-            }
-
-            // 2. Create another node that will be grafted between two existing nodes, then graft
-            //    `node` to it.
-            //
-            // Note: given that `prev_in_tree` has children and that `node` is not an ancestor of
-            // any of the children of `prev_in_tree`, we know that `node` is on a different fork to
-            // all of the children of `prev_in_tree`.
-            if node.parent_hash.is_none() {
-                for child_link in &prev_in_tree.children {
-                    let child_hash = child_link.hash;
-                    // Find the highest (by slot) common ancestor between `node` and `child`.
-                    //
-                    // The common ancestor is the last block before `node` and `child` forked.
-                    let ancestor_hash =
-                        self.find_highest_common_ancestor(node.block_hash, child_hash)?;
-
-                    // If the block before `node` and `child` forked is _not_ `prev_in_tree` we
-                    // must add this new block into the tree (because it is a decision node
-                    // between two forks).
-                    if ancestor_hash != prev_in_tree.block_hash {
-                        // Create a new `common_ancestor` node which represents the `ancestor_hash`
-                        // block, has `prev_in_tree` as the parent and has both `node` and `child`
-                        // as children.
-                        let common_ancestor = Node {
-                            parent_hash: Some(prev_in_tree.block_hash),
-                            children: vec![
-                                ChildLink {
-                                    hash: node.block_hash,
-                                    successor_slot: self.find_ancestor_successor_slot(
-                                        ancestor_hash,
-                                        node.block_hash,
-                                    )?,
-                                },
-                                ChildLink {
-                                    hash: child_hash,
-                                    successor_slot: self
-                                        .find_ancestor_successor_slot(ancestor_hash, child_hash)?,
-                                },
-                            ],
-                            ..Node::new(ancestor_hash)
-                        };
-
-                        let child = self.get_mut_node(child_hash)?;
-
-                        // Graft `child` and `node` to `common_ancestor`.
-                        child.parent_hash = Some(common_ancestor.block_hash);
-                        node.parent_hash = Some(common_ancestor.block_hash);
-
-                        // Detach `child` from `prev_in_tree`, replacing it with `common_ancestor`.
-                        prev_in_tree.replace_child_hash(child_hash, common_ancestor.block_hash)?;
-
-                        // Store the new `common_ancestor` node.
-                        self.nodes
-                            .insert(common_ancestor.block_hash, common_ancestor);
-
-                        break;
-                    }
-                }
-            }
-        }
-
-        if node.parent_hash.is_none() {
-            // 3. Graft `node` to an existing node.
-            //
-            // Graft `node` to `prev_in_tree` and `prev_in_tree` to `node`
-            node.parent_hash = Some(prev_in_tree.block_hash);
-            prev_in_tree.children.push(ChildLink {
-                hash: node.block_hash,
-                successor_slot: self
-                    .find_ancestor_successor_slot(prev_in_tree.block_hash, node.block_hash)?,
-            });
-        }
-
-        // Update `prev_in_tree`. A mutable reference was not maintained to satisfy the borrow
-        // checker. Perhaps there's a better way?
-        self.nodes.insert(prev_in_tree.block_hash, prev_in_tree);
-        self.nodes.insert(node.block_hash, node);
-
-        Ok(())
-    }
-
-    /// For the given block `hash`, find its highest (by slot) ancestor that exists in the reduced
-    /// tree.
-    fn find_prev_in_tree(&mut self, node: &Node) -> Option<Hash256> {
-        self.iter_ancestors(node.block_hash, false)
-            .take_while(|(_, slot)| *slot >= self.root_slot())
-            .find(|(root, _)| self.nodes.contains_key(root))
-            .map(|(root, _)| root)
-    }
-
-    /// For the two given block roots (`a_root` and `b_root`), find the first block they share in
-    /// the tree. Viz, find the block that these two distinct blocks forked from.
-    fn find_highest_common_ancestor(&self, a_root: Hash256, b_root: Hash256) -> Result<Hash256> {
-        let mut a_iter = self
-            .iter_ancestors(a_root, false)
-            .take_while(|(_, slot)| *slot >= self.root_slot());
-        let mut b_iter = self
-            .iter_ancestors(b_root, false)
-            .take_while(|(_, slot)| *slot >= self.root_slot());
-
-        // Combines the `next()` fns on the `a_iter` and `b_iter` and returns the roots of two
-        // blocks at the same slot, or `None` if we have gone past genesis or the root of this tree.
-        let mut iter_blocks_at_same_height = || -> Option<(Hash256, Hash256)> {
-            match (a_iter.next(), b_iter.next()) {
-                (Some((mut a_root, a_slot)), Some((mut b_root, b_slot))) => {
-                    // If either of the slots are lower than the root of this tree, exit early.
-                    if a_slot < self.root.1 || b_slot < self.root.1 {
-                        None
-                    } else {
-                        match a_slot.cmp(&b_slot) {
-                            Ordering::Less => {
-                                for _ in a_slot.as_u64()..b_slot.as_u64() {
-                                    b_root = b_iter.next()?.0;
-                                }
-                            }
-                            Ordering::Greater => {
-                                for _ in b_slot.as_u64()..a_slot.as_u64() {
-                                    a_root = a_iter.next()?.0;
-                                }
-                            }
-                            Ordering::Equal => (),
-                        }
-                        Some((a_root, b_root))
-                    }
-                }
-                _ => None,
-            }
-        };
-
-        loop {
-            match iter_blocks_at_same_height() {
-                Some((a_root, b_root)) if a_root == b_root => break Ok(a_root),
-                Some(_) => (),
-                None => break Err(Error::NoCommonAncestor((a_root, b_root))),
-            }
-        }
-    }
-
-    /// Return an iterator from the given `block_root` back to finalization.
-    ///
-    /// If `include_latest` is true, then the hash and slot for `block_root` will be included.
-    pub fn iter_ancestors<'a>(
-        &'a self,
-        block_root: Hash256,
-        include_latest: bool,
-    ) -> impl Iterator<Item = (Hash256, Slot)> + 'a {
-        self.block_root_tree
-            .every_slot_iter_from(block_root)
-            .skip(if include_latest { 0 } else { 1 })
-    }
-
-    /// Verify the integrity of `self`. Returns `Ok(())` if the tree has integrity, otherwise returns `Err(description)`.
-    ///
-    /// Tries to detect the following erroneous conditions:
-    ///
-    /// - Dangling references inside the tree.
-    /// - Any scenario where there's not exactly one root node.
-    ///
-    /// ## Notes
-    ///
-    /// Computationally intensive, likely only useful during testing.
-    pub fn verify_integrity(&self) -> std::result::Result<(), String> {
-        let num_root_nodes = self
-            .nodes
-            .iter()
-            .filter(|(_key, node)| node.parent_hash.is_none())
-            .count();
-
-        if num_root_nodes != 1 {
-            return Err(format!(
-                "Tree has {} roots, should have exactly one.",
-                num_root_nodes
-            ));
-        }
-
-        let verify_node_exists = |key: Hash256, msg: String| -> std::result::Result<(), String> {
-            if self.nodes.contains_key(&key) {
-                Ok(())
-            } else {
-                Err(msg)
-            }
-        };
-
-        // Iterate through all the nodes and ensure all references they store are valid.
-        self.nodes
-            .iter()
-            .map(|(_key, node)| {
-                if let Some(parent_hash) = node.parent_hash {
-                    verify_node_exists(parent_hash, "parent must exist".to_string())?;
-                }
-
-                node.children
-                    .iter()
-                    .map(|child| {
-                        verify_node_exists(child.hash, "child_must_exist".to_string())?;
-
-                        if self.find_ancestor_successor_slot(node.block_hash, child.hash)?
-                            == child.successor_slot
-                        {
-                            Ok(())
-                        } else {
-                            Err("successor slot on child link is incorrect".to_string())
-                        }
-                    })
-                    .collect::<std::result::Result<(), String>>()?;
-
-                verify_node_exists(node.block_hash, "block hash must exist".to_string())?;
-
-                Ok(())
-            })
-            .collect::<std::result::Result<(), String>>()?;
-
-        Ok(())
-    }
-
-    fn get_node(&self, hash: Hash256) -> Result<&Node> {
-        self.nodes
-            .get(&hash)
-            .ok_or_else(|| Error::MissingNode(hash))
-    }
-
-    fn get_mut_node(&mut self, hash: Hash256) -> Result<&mut Node> {
-        self.nodes
-            .get_mut(&hash)
-            .ok_or_else(|| Error::MissingNode(hash))
-    }
-
-    fn get_block(&self, block_root: Hash256) -> Result<BeaconBlock<E>> {
-        self.store
-            .get::<BeaconBlock<E>>(&block_root)?
-            .ok_or_else(|| Error::MissingBlock(block_root))
-    }
-
-    fn root_slot(&self) -> Slot {
-        self.root.1
-    }
-
-    fn as_bytes(&self) -> Vec<u8> {
-        let reduced_tree_ssz = ReducedTreeSsz::from_reduced_tree(&self);
-        reduced_tree_ssz.as_ssz_bytes()
-    }
-
-    fn from_bytes(
-        bytes: &[u8],
-        store: Arc<T>,
-        block_root_tree: Arc<BlockRootTree>,
-    ) -> Result<Self> {
-        let reduced_tree_ssz = ReducedTreeSsz::from_ssz_bytes(bytes)?;
-        Ok(reduced_tree_ssz.into_reduced_tree(store, block_root_tree)?)
-    }
-}
-
-#[derive(Debug, Clone, PartialEq, Encode, Decode)]
-pub struct Node {
-    /// Hash of the parent node in the reduced tree (not necessarily parent block).
-    pub parent_hash: Option<Hash256>,
-    pub children: Vec<ChildLink>,
-    pub weight: u64,
-    pub block_hash: Hash256,
-    pub voters: Vec<usize>,
-}
-
-#[derive(Default, Clone, Debug, PartialEq, Encode, Decode)]
-pub struct ChildLink {
-    /// Hash of the child block (may not be a direct descendant).
-    pub hash: Hash256,
-    /// Slot of the block which is a direct descendant on the chain leading to `hash`.
-    ///
-    /// Node <--- Successor <--- ... <--- Child
-    pub successor_slot: Slot,
-}
-
-impl Node {
-    pub fn new(block_hash: Hash256) -> Self {
-        Self {
-            parent_hash: None,
-            children: vec![],
-            weight: 0,
-            block_hash,
-            voters: vec![],
-        }
-    }
-
-    /// Replace a child with a new child, whilst preserving the successor slot.
-    ///
-    /// The new child should have the same ancestor successor block as the old one.
-    pub fn replace_child_hash(&mut self, old: Hash256, new: Hash256) -> Result<()> {
-        let i = self
-            .children
-            .iter()
-            .position(|c| c.hash == old)
-            .ok_or_else(|| Error::MissingChild(old))?;
-        self.children[i].hash = new;
-
-        Ok(())
-    }
-
-    pub fn remove_child(&mut self, child: Hash256) -> Result<()> {
-        let i = self
-            .children
-            .iter()
-            .position(|c| c.hash == child)
-            .ok_or_else(|| Error::MissingChild(child))?;
-
-        self.children.remove(i);
-
-        Ok(())
-    }
-
-    pub fn remove_voter(&mut self, voter: usize) -> Option<usize> {
-        let i = self.voters.iter().position(|&v| v == voter)?;
-        Some(self.voters.remove(i))
-    }
-
-    pub fn add_voter(&mut self, voter: usize) {
-        self.voters.push(voter);
-    }
-
-    pub fn has_votes(&self) -> bool {
-        !self.voters.is_empty()
-    }
-}
-
-#[derive(Debug, Clone, Copy, PartialEq, Encode, Decode)]
-pub struct Vote {
-    hash: Hash256,
-    slot: Slot,
-}
-
-/// A Vec-wrapper which will grow to match any request.
-///
-/// E.g., a `get` or `insert` to an out-of-bounds element will cause the Vec to grow (using
-/// Default) to the smallest size required to fulfill the request.
-#[derive(Default, Clone, Debug, PartialEq)]
-pub struct ElasticList<T>(Vec<T>);
-
-impl<T> ElasticList<T>
-where
-    T: Default,
-{
-    fn ensure(&mut self, i: usize) {
-        if self.0.len() <= i {
-            self.0.resize_with(i + 1, Default::default);
-        }
-    }
-
-    pub fn get(&mut self, i: usize) -> &T {
-        self.ensure(i);
-        &self.0[i]
-    }
-
-    pub fn get_ref(&self, i: usize) -> Option<&T> {
-        self.0.get(i)
-    }
-
-    pub fn insert(&mut self, i: usize, element: T) {
-        self.ensure(i);
-        self.0[i] = element;
-    }
-}
-
-impl From<Error> for String {
-    fn from(e: Error) -> String {
-        format!("{:?}", e)
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use store::MemoryStore;
-    use types::eth_spec::MinimalEthSpec;
-
-    #[test]
-    fn test_reduced_tree_ssz() {
-        let store = Arc::new(MemoryStore::<MinimalEthSpec>::open());
-        let block_root_tree = Arc::new(BlockRootTree::new(Hash256::zero(), Slot::new(0)));
-        let tree = ReducedTree::new(
-            store.clone(),
-            block_root_tree.clone(),
-            &BeaconBlock::empty(&MinimalEthSpec::default_spec()),
-            Hash256::zero(),
-        );
-        let ssz_tree = ReducedTreeSsz::from_reduced_tree(&tree);
-        let bytes = tree.as_bytes();
-        let recovered_tree = ReducedTree::from_bytes(&bytes, store, block_root_tree).unwrap();
-
-        let recovered_ssz = ReducedTreeSsz::from_reduced_tree(&recovered_tree);
-        assert_eq!(ssz_tree, recovered_ssz);
-    }
-}