reserve D for non empty set;
reserve s for FinSequence of D;
reserve m,n for Element of NAT;

theorem Th8:
  1 <= len s implies
  Op-RightShift(s) is FinSequence of D
  proof
    assume 1 <= len s;
    then len s in Seg (len s);
    then len s in dom s by FINSEQ_1:def 3;
    then s.(len s) is Element of D by FINSEQ_2:11;
    then <* s.(len s) *> is FinSequence of D by FINSEQ_1:74;
    then reconsider ss=((<* s.(len s) *>) ^ s )
    as FinSequence of D by FINSEQ_1:75;
    ss | (len s) is FinSequence of D;
    hence thesis;
  end;
