Given a boolean combination circuit composed of AND, OR, and NOT gates, is it satisfiable?

CIRCUIT-SAT = {C C is a satisfiable boolean
combinational circuit}

where C is a binary-string encoding of the circuit (e.g., as a graph)

Determining membership in CIRCUIT-SAT would require checking the
2^{k} possible binary assignments to the k inputs of a circuit.

There is strong evidence that CIRCUIT-SAT P.