let Y be non empty set ; :: thesis: for a, b being Function of Y,BOOLEAN holds a '<' a 'or' b
let a, b be Function of Y,BOOLEAN; :: thesis: a '<' a 'or' b
a 'imp' (a 'or' b) = I_el Y by Th26;
hence a '<' a 'or' b by BVFUNC_1:16; :: thesis: verum