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

theorem Th24:
  for a, b being Element of Benzene holds a [= b iff a c= b
proof
  let a, b be Element of Benzene;
  reconsider x = a, y = b as Element of B_6 by Th9,YELLOW_1:1;
  hereby
    assume a [= b;
    then x <= y by Th13;
    hence a c= b by YELLOW_1:3;
  end;
  assume a c= b;
  then x <= y by YELLOW_1:3;
  hence thesis by Th13;
end;
