
theorem Th58:
  for L being non empty RelStr, S being non empty SubRelStr of L
  for x being Element of S holds x is Element of L
proof
  let L be non empty RelStr, S be non empty SubRelStr of L;
  let x be Element of S;
  x in the carrier of S & the carrier of S c= the carrier of L by Def13;
  hence thesis;
end;
