theorem Th79:
  for p,q being XFinSequence of D st p c= q
    ex r being XFinSequence of D st p^r = q
proof
 let p,q being XFinSequence of D;
 assume p c= q;
  then consider r such that
A1: p^r = q by Th78;
  reconsider r as XFinSequence of D by A1,AFINSQ_1:31;
 take r;
 thus thesis by A1;
end;
