# Variables
ErrFutureBlock is returned when a block's timestamp is in the future according to the current node.
ErrInvalidNumber is returned if a block's number doesn't equal its parent's plus one.
ErrPrunedAncestor is returned when validating a block requires an ancestor that is known, but the state of which is not available.
ErrUnknownAncestor is returned when validating a block requires an ancestor that is unknown.
# Interfaces
ChainHeaderReader defines a small collection of methods needed to access the local blockchain during header verification.
ChainReader defines a small collection of methods needed to access the local blockchain during header and/or uncle verification.
Engine is an algorithm agnostic consensus engine.