**a implies b**and its contrapositive

**not b implies not a**. Also shown are the statements

**not a or b**and

**not a or not not b**:

a | b | not a | not b | a --> b | not b --> not a | not a or b | not a or not not b ------------------------------------------------------------------------------------- T | T | F | F | T | T | T | T T | F | F | T | F | F | F | F F | T | T | F | T | T | T | T F | F | T | T | T | T | T | TNote also converse and inverse. Just as an implication is logically equivalent to its contrapositive, the converse of the implication is logically equivalent to its inverse. When considering a proof, the contrapositive may be an easier thing to prove than the original implication, for whatever reason.