reserve i,j,k,l,m,n for Nat,
  D for non empty set,
  f for FinSequence of D;
reserve X for compact Subset of TOP-REAL 2;
reserve r for Real;

theorem Th26:
  for f being non trivial FinSequence of TOP-REAL 2 holds <*
  NW-corner L~f*> is_in_the_area_of f
proof
  let f be non trivial FinSequence of TOP-REAL 2;
  set g = <*NW-corner L~f*>;
  let n;
  assume
A1: n in dom g;
  dom g = {1} by FINSEQ_1:2,38;
  then n = 1 by A1,TARSKI:def 1;
  then g/.n = |[W-bound L~f, N-bound L~f]| by FINSEQ_4:16;
  then (g/.n)`1 = W-bound L~f & (g/.n)`2 = N-bound L~f by EUCLID:52;
  hence thesis by SPRECT_1:21,22;
end;
