User:Silence/Logic2

~(~P ~Q), ~(P ~R), ~(Q ~R) ⊢ R ~(~P ~Q), ~(~R P), ~(~R Q) ⊢ R  

~P → Q, ~P ∨ R, ~Q ∨ R ⊢ R ~P → Q, R ∨ ~P, R ∨ ~Q ⊢ R

P ∨ Q, P → R, Q → R ⊢ R Proof by Cases P ∨ Q, ~R → ~P, ~R → ~Q ⊢ R