reserve Y for non empty set;
reserve Y for non empty set;
reserve Y for non empty set;
reserve Y for non empty set,
  a,b,c,d,e,f,g for Function of Y,BOOLEAN;

theorem
  ((a 'imp' c) 'or' (b 'imp' c)) '&' (a '&' b) '<' c
proof
  (a 'imp' c) 'or' (b 'imp' c) = (a '&' b) 'imp' c by Th76;
  hence thesis by Th2;
end;
