 reserve U for set,
         X, Y for Subset of U;
 reserve U for non empty set,
         A, B, C for non empty IntervalSet of U;
 reserve X for Tolerance_Space,
         A, B, C for RoughSet of X;

theorem Th66:
  A _/\_ (B _\/_ C) = (A _/\_ B) _\/_ (A _/\_ C) by XBOOLE_1:23;
