reserve S for Subset of TOP-REAL 2,
  C,C1,C2 for non empty compact Subset of TOP-REAL 2,
  p,q for Point of TOP-REAL 2;
reserve i,j,k for Nat,
  t,r1,r2,s1,s2 for Real;
reserve D1 for non vertical non empty compact Subset of TOP-REAL 2,
  D2 for non horizontal non empty compact Subset of TOP-REAL 2,
  D for non vertical non horizontal non empty compact Subset of TOP-REAL 2;

theorem Th64:
  SW-corner L~SpStSeq C = SW-corner C
proof
  thus SW-corner L~SpStSeq C = |[W-bound C, S-bound L~SpStSeq C]| by Th58
    .= SW-corner C by Th59;
end;
