1. The problem statement, all variables and given/known data I'm trying to show that controlled-not gate can not be used to make toffolit gate(controlled-controlled not gate) 2. Relevant equations 3. The attempt at a solution i'm thinking that controlled not only has +(addition modulo 2) of the inputs, it cant make X and Y for input X,Y hence cannot make function XY+Z but I'm not sure if this is right, and I don't know how else to go about this problem. thanks