Open Problems Column

Notation 3.1 As usual the term circuit means family of circuits, one for each n. All circuits will alternate AND and OR gates. There will be no NOT gates; however, both inputs and their negations are available. The depth of a circuit is the longest path from input to output. The fan-in of a circuit is the max number of inputs to a gate. The size of a circuit is the number of gates. A (d, f, s) circuit is a circuit of depth d, fan-in f , and size s. Note that f ≤ s so unbounded fanin really means f = s. Note also that s ≤ fd. It is clear what it means for a circuit to compute a function g : {0, 1}n → {0, 1}k.