A Boolean (combinatoiral) circuit is a labeled (with the labels: AND, OR, NOT, IN, OUT), directed, acyclic graph, that satisfies:
- fan-in=2 for the AND and OR nodes
- fan-n=1 for the NOT nodes
- fan-in=0 for the IN nodes
- fan-out=0 to exactly one node (the OUT node)
- Unbounded fan-out to the rest of the nodes (but the OUT node)
A Boolean formula is a Boolean circuits with fan-out $\leq$ 1 to all of the nodes.
Let us denote by $C(T(n))$ the class of all languages recognizable by n-bit formulas of size (in the meaning of Boolean circutit size) at most T(n).
Let us denote by $\text{Size}(T(n))$ the class of all languages recognizable by n-bit Boolean circuits of size at most $T(n)$.
- What is the relationship between $C(T(n))$ and $\text{Size}(T(n))$?
- Is $C(T(n))$ a well-known class? What is its name in the literature?