reserve k,n for Nat,
  x,y,z,y1,y2 for object,X,Y for set,
  f,g for Function;
reserve p,q,r,s,t for XFinSequence;

theorem Th11:
  for D being set, f being XFinSequence of D holds f is PartFunc of NAT,D
proof
  let D be set, f be XFinSequence of D;
  dom f c= NAT & rng f c= D by RELAT_1:def 19;
  hence thesis by RELSET_1:4;
end;
