The XOR operator is a Boolean operator, its principle is that when the inputs are equal the result is zero, and when the inputs are non-equal the result is one. (when more than two inputs are involved the inputs must be separated to two at time)
Following the truth table:
0 ^ 0 = 0 0 ^ 1 = 1 1 ^ 0 = 1 1 ^ 1 = 0
This operator is the opposite of XOR, it negates the result of the XOR operator.
Following the truth table:
~ (0 ^ 0) = 1 ~ (0 ^ 1) = 0 ~ (1 ^ 0) = 0 ~ (1 ^ 1) = 1
Those operators can be easily implemented by a few transistors.