reserve i, j, n for Element of NAT,
  f, g, h, k for FinSequence of REAL,
  M, N for non empty MetrSpace;

theorem Th9:
  len f = len abs f & dom f = dom abs f
proof
  rng f c= REAL & dom absreal = REAL by FUNCT_2:def 1;
  hence len f = len abs f by FINSEQ_2:29;
  hence thesis by FINSEQ_3:29;
end;
