Before revision: Integrated circuits have two primary classes of mask sets: 1. base layers that are used to build the structures that make up the logic such as transistors, and 2: metal layers that connect the logic together .
After revision: Integrated circuits have two primary classes of mask sets: firstly, "base" layers that are used to build the structures , such as transistors, that comprise circuit logic and, secondly, "metal" layers that connect the circuit logic .