theorem Th9:
  for D being set, e1,e2 being FinSequence of D holds ex e being
  FinSequence of D* st len e = n & for i be Nat st i in Seg n holds (i in Seg k
  implies e.i = e1) & (not i in Seg k implies e.i = e2)
proof
  let D be set, e1,e2 be FinSequence of D;
  e1 in D* & e2 in D* by FINSEQ_1:def 11;
  hence thesis by Th2;
end;
