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diff --git a/consensus/consensus.go b/consensus/consensus.go
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+// Copyright 2017 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+// Package consensus implements different Ethereum consensus engines.
+package consensus
+
+import (
+	"math/big"
+
+	"github.com/ava-labs/coreth/core/state"
+	"github.com/ava-labs/coreth/core/types"
+	"github.com/ava-labs/coreth/params"
+	"github.com/ava-labs/coreth/rpc"
+	"github.com/ava-labs/go-ethereum/common"
+)
+
+// ChainReader defines a small collection of methods needed to access the local
+// blockchain during header and/or uncle verification.
+type ChainReader interface {
+	// Config retrieves the blockchain's chain configuration.
+	Config() *params.ChainConfig
+
+	// CurrentHeader retrieves the current header from the local chain.
+	CurrentHeader() *types.Header
+
+	// GetHeader retrieves a block header from the database by hash and number.
+	GetHeader(hash common.Hash, number uint64) *types.Header
+
+	// GetHeaderByNumber retrieves a block header from the database by number.
+	GetHeaderByNumber(number uint64) *types.Header
+
+	// GetHeaderByHash retrieves a block header from the database by its hash.
+	GetHeaderByHash(hash common.Hash) *types.Header
+
+	// GetBlock retrieves a block from the database by hash and number.
+	GetBlock(hash common.Hash, number uint64) *types.Block
+}
+
+// Engine is an algorithm agnostic consensus engine.
+type Engine interface {
+	// Author retrieves the Ethereum address of the account that minted the given
+	// block, which may be different from the header's coinbase if a consensus
+	// engine is based on signatures.
+	Author(header *types.Header) (common.Address, error)
+
+	// VerifyHeader checks whether a header conforms to the consensus rules of a
+	// given engine. Verifying the seal may be done optionally here, or explicitly
+	// via the VerifySeal method.
+	VerifyHeader(chain ChainReader, header *types.Header, seal bool) error
+
+	// VerifyHeaders is similar to VerifyHeader, but verifies a batch of headers
+	// concurrently. The method returns a quit channel to abort the operations and
+	// a results channel to retrieve the async verifications (the order is that of
+	// the input slice).
+	VerifyHeaders(chain ChainReader, headers []*types.Header, seals []bool) (chan<- struct{}, <-chan error)
+
+	// VerifyUncles verifies that the given block's uncles conform to the consensus
+	// rules of a given engine.
+	VerifyUncles(chain ChainReader, block *types.Block) error
+
+	// VerifySeal checks whether the crypto seal on a header is valid according to
+	// the consensus rules of the given engine.
+	VerifySeal(chain ChainReader, header *types.Header) error
+
+	// Prepare initializes the consensus fields of a block header according to the
+	// rules of a particular engine. The changes are executed inline.
+	Prepare(chain ChainReader, header *types.Header) error
+
+	// Finalize runs any post-transaction state modifications (e.g. block rewards)
+	// but does not assemble the block.
+	//
+	// Note: The block header and state database might be updated to reflect any
+	// consensus rules that happen at finalization (e.g. block rewards).
+	Finalize(chain ChainReader, header *types.Header, state *state.StateDB, txs []*types.Transaction,
+		uncles []*types.Header)
+
+	// FinalizeAndAssemble runs any post-transaction state modifications (e.g. block
+	// rewards) and assembles the final block.
+	//
+	// Note: The block header and state database might be updated to reflect any
+	// consensus rules that happen at finalization (e.g. block rewards).
+	FinalizeAndAssemble(chain ChainReader, header *types.Header, state *state.StateDB, txs []*types.Transaction,
+		uncles []*types.Header, receipts []*types.Receipt) (*types.Block, error)
+
+	// Seal generates a new sealing request for the given input block and pushes
+	// the result into the given channel.
+	//
+	// Note, the method returns immediately and will send the result async. More
+	// than one result may also be returned depending on the consensus algorithm.
+	Seal(chain ChainReader, block *types.Block, results chan<- *types.Block, stop <-chan struct{}) error
+
+	// SealHash returns the hash of a block prior to it being sealed.
+	SealHash(header *types.Header) common.Hash
+
+	// CalcDifficulty is the difficulty adjustment algorithm. It returns the difficulty
+	// that a new block should have.
+	CalcDifficulty(chain ChainReader, time uint64, parent *types.Header) *big.Int
+
+	// APIs returns the RPC APIs this consensus engine provides.
+	APIs(chain ChainReader) []rpc.API
+
+	// Close terminates any background threads maintained by the consensus engine.
+	Close() error
+
+	ExtraStateChange(block *types.Block, statedb *state.StateDB) error
+}
+
+// PoW is a consensus engine based on proof-of-work.
+type PoW interface {
+	Engine
+
+	// Hashrate returns the current mining hashrate of a PoW consensus engine.
+	Hashrate() float64
+}