%%% A few theorems in classical propositional logic
%%% (taken from F. J. Pelletier, "75 Problems for Testing ATP")
%%% Author: Roberto Virga

%query 1 *
theorem ((P => Q) <=> (! Q => ! P)).

%query 1 *
theorem (! ! P <=> P).

%query 1 * 
theorem ((! (P => Q)) => (Q => P)).

%query 1 *
theorem ((! P => Q) => (! Q => P)).

%query 1 *
theorem (((P | Q) => (P | R)) => (P | (Q => R))).

%query 1 *
theorem (P | ! P).

%query 1 *
theorem (P | ! ! ! P).

%query 1 *
theorem (((P => Q) => P) => P).

%query 1 *
theorem (((P | Q) & (! P | Q) &
            (P | ! Q)) => ! (! P | ! Q)).

%query 1 *
theorem ((Q => R) &
         (R => (P & Q)) &
         (P => (Q | R)) => (P <=> Q)).

%query 1 *
theorem (P <=> P).

%query 1 *
theorem (((P <=> Q) <=> R) <=> (P <=> (Q <=> R))). 

%query 1 *
theorem ((P | (Q & R)) <=> ((P | Q) &
           (P | R))).

%query 1 *
theorem ((P <=> Q) <=> ((Q | ! P) &
           (! Q | P))).

%query 1 *
theorem ((P => Q) <=> (! P | Q)).

%query 1 *
theorem ((P => Q) | (Q => P)).

%query 1 *
theorem (((P & (Q => R)) => S) <=>
            ((! P | Q | S) &
             (! P | ! R | S))).