let Y be non empty set ; :: thesis: for a, b, c being Element of Funcs Y,BOOLEAN holds (a 'imp' b) '&' (a 'imp' c) '<' a 'imp' (b '&' c)
let a, b, c be Element of Funcs Y,BOOLEAN ; :: thesis: (a 'imp' b) '&' (a 'imp' c) '<' a 'imp' (b '&' c)
(a 'imp' b) '&' (a 'imp' c) '<' (a '&' a) 'imp' (b '&' c) by Th19;
hence (a 'imp' b) '&' (a 'imp' c) '<' a 'imp' (b '&' c) ; :: thesis: verum