122 (-a) × (-a) = a × a 2017-09-26T22:25:54.850

38 (A → B) → (¬B → ¬A) 2018-04-03T15:31:51.943

22 Existential Golf 2018-07-13T16:39:34.747

21 Prove DeMorgan's laws 2016-10-16T08:13:41.340