reserve L for Boolean non empty RelStr;
reserve a,b,c,d for Element of L;

theorem
  a <= b\a implies a = Bottom L
proof
  assume
A1: a <= b\a;
  (b"/\"'not' a) "/\" a = b"/\"('not' a"/\"a) by LATTICE3:16
    .= b"/\"Bottom L by Th34
    .= Bottom L by WAYBEL_1:3;
  hence thesis by A1,Th10;
end;
