
theorem
  for H being non empty RelStr st H is Heyting for a,b,c being Element
  of H st b <= c holds (a => b) <= (a => c)
proof
  let H be non empty RelStr;
  assume
A1: H is Heyting;
  let a,b,c be Element of H;
  assume
A2: b <= c;
  a"/\"(a => b) <= b by A1,Lm5;
  then a"/\"(a => b) <= c by A1,A2,ORDERS_2:3;
  hence thesis by A1,Th67;
end;
