
theorem Th67:
  for H being non empty RelStr st H is Heyting for x,a,y being
  Element of H holds x >= a "/\" y iff a => x >= y
proof
  let H be non empty RelStr;
  assume
A1: H is Heyting;
  let x,a,y be Element of H;
  [a =>, a "/\"] is Galois by A1,Def20;
  then x >= (a "/\").y iff (a =>).x >= y by A1,Th8;
  hence thesis by Def18;
end;
