let Y be non empty set ; :: thesis: for a, b being Element of Funcs (Y,BOOLEAN) holds ((a 'imp' b) '&' a) 'imp' b = I_el Y
let a, b be Element of Funcs (Y,BOOLEAN); :: thesis: ((a 'imp' b) '&' a) 'imp' b = I_el Y
((a 'imp' b) '&' a) 'imp' b = (a '&' b) 'imp' b by BVFUNC_7:10;
hence ((a 'imp' b) '&' a) 'imp' b = I_el Y by BVFUNC_6:40; :: thesis: verum