Our Basic Inference Rules p→q p q [→E] p&q p [&E] p p ∨ q [∨I] p↔q p → q [↔E] p&q q [&E] q p ∨ q [∨I] p↔q q → p [↔E] ~~p p [~E] p q p & q [&I] p∨q p→r q→r r [∨E] p→q q→p p ↔ q [↔I] p . . . q p → q [→I] ~p p . . . q&~q [~I]