let Y be non empty set ; :: thesis: for a, c, b being Element of Funcs Y,BOOLEAN holds (a 'imp' c) '&' (b 'imp' c) '<' (a 'or' b) 'imp' c
let a, c, b be Element of Funcs Y,BOOLEAN ; :: thesis: (a 'imp' c) '&' (b 'imp' c) '<' (a 'or' b) 'imp' c
((a 'imp' c) '&' (b 'imp' c)) 'imp' ((a 'or' b) 'imp' c) = I_el Y by BVFUNC_6:9;
hence (a 'imp' c) '&' (b 'imp' c) '<' (a 'or' b) 'imp' c by BVFUNC_1:19; :: thesis: verum