
theorem Th3:
  for R being RelStr, x being set holds (the InternalRel of R)-Seg
  x c= the carrier of R
proof
  let R be RelStr, x be set;
  set r = the InternalRel of R, c = the carrier of R;
  r-Seg x c= field r & field r c= c \/ c by RELSET_1:8,WELLORD1:9;
  hence thesis;
end;
