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) '&' (b 'imp' c) '&' (a 'or' b) '<' c
proof
  set K1 = (a 'imp' c) '&' (b 'imp' c);
  K1 '<' (a 'or' b) 'imp' c by Th20;
  then
A1: K1 '&' (a 'or' b) '<' ((a 'or' b) 'imp' c) '&' (a 'or' b) by Th33;
  ((a 'or' b) 'imp' c) '&' (a 'or' b) '<' c by Th2;
  hence thesis by A1,BVFUNC_1:15;
end;
