'Used by the verifier when a reorg has happened'

def undo_verifications(self, blockchain, height):

    txs = set()
    with self.lock:
        for (tx_hash, item) in self.verified_tx.items():
            (tx_height, timestamp, pos) = item
            if (tx_height >= height):
                header = blockchain.read_header(tx_height)
                if ((not header) or (header.get('timestamp') != timestamp)):
                    self.verified_tx.pop(tx_hash, None)
                    txs.add(tx_hash)
    return txs
