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 Th62:
  NW-corner L~SpStSeq C = NW-corner C
proof
  thus NW-corner L~SpStSeq C = |[W-bound C, N-bound L~SpStSeq C]| by Th58
    .= NW-corner C by Th60;
end;
