let Y be non empty set ; :: thesis: for a, b, c being Function of Y,BOOLEAN holds ((a 'imp' c) 'or' (b 'imp' c)) '&' (a '&' b) '<' c
let a, b, c be Function of Y,BOOLEAN; :: thesis: ((a 'imp' c) 'or' (b 'imp' c)) '&' (a '&' b) '<' c
(a 'imp' c) 'or' (b 'imp' c) = (a '&' b) 'imp' c by Th76;
hence ((a 'imp' c) 'or' (b 'imp' c)) '&' (a '&' b) '<' c by Th2; :: thesis: verum