(=> or a thin right arrow) A binary Boolean function and logical connective. A => B is true unless A is true and B is false. The truth table is

        A B | A => B
        ----+-------
        F F |   T
        F T |   T
        T F |   F
        T T |   T

It is surprising at first that A => B is always true if A is false, but if X => Y then we would expect that (X & Z) => Y for any Z.