
theorem Th72:
  for H being non empty RelStr st H is Heyting for a,b being
  Element of H holds b <= (a => b)
proof
  let H be non empty RelStr;
  assume
A1: H is Heyting;
  let a,b be Element of H;
  a"/\"b <= b by A1,YELLOW_0:23;
  hence thesis by A1,Th67;
end;
