Redstone circuits/Logic/NOR

A device where the output is off when at least one of the inputs are on. All logic gates can be made from some combinations if the NOR and NAND gates. In Minecraft, NOR is a basic logic gate, implemented by a torch with two or more inputs. (A torch with 1 input is the NOT gate, and with no inputs is the TRUE gate, that is, a power source.)

A torch can easily accommodate 3 mutually isolated inputs, as in design A. Design B goes to greater lengths to squeeze in a fourth input. If more inputs are necessary, it is simplest to use OR gates to combine them, then use an inverter (NOT) at the end. It is also possible to combine OR and NOR gates, according to the Boolean formula A ⊽ B ⊽ C = A ⊽ ¬(B ∨ C). (Either way, the nested gates will cost a few extra ticks.)