reserve L for Ortholattice,
  a, b, c for Element of L;

theorem Th19:
  for a, b being Element of Benzene st a = 3 \ 1 & b = 2 holds a
  "\/" b = 3 & a "/\" b = 0
proof
  let a,b be Element of Benzene;
  assume
A1: a = 3\1 & b = 2;
  then
  a in { 0, 1, 3 \ 1, 2, 3 \ 2, 3 } & b in { 0, 1, 3 \ 1, 2, 3 \ 2, 3 } by
ENUMSET1:def 4;
  then reconsider aa = a, bb = b as Element of B_6 by YELLOW_1:1;
  aa "\/" bb = 3 & aa "/\" bb = 0 by A1,Th15;
  hence thesis by Th14;
end;
