reserve p,q,r,s for boolean object;

theorem
  p '&' q 'or' q '&' r 'or' r '&' p = (p 'or' q) '&' (q 'or' r) '&' (r 'or' p)
proof
A1: q = FALSE or q = TRUE by Def3;
  p = FALSE or p = TRUE by Def3;
  hence thesis by A1;
end;
