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;

theorem Th16:
  for f being FinSequence of TOP-REAL 2 holds dom Y_axis f = dom f
proof
  let f be FinSequence of TOP-REAL 2;
  len Y_axis f = len f by GOBOARD1:def 2;
  hence thesis by FINSEQ_3:29;
end;
