class BlockTree {

  public UInt64 getEpoch(Bytes32 blockRoot) {
    assertBlockIsInTree(blockRoot);
    final UInt64 slot = blockRootToSlot.get(blockRoot);
    return compute_epoch_at_slot(slot);
  }

  private  BlockTree(final HashTree hashTree, final Map<Bytes32, UInt64> blockRootToSlot);

}