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

theorem Th7:
  for s be FinSequence holds len (Op-RightShift(s)) = len s
  proof
    let s be FinSequence;
    A1: len <* s.(len s) *> = 1 by FINSEQ_1:40;
    len ((<* s.(len s) *>) ^ s ) = (len s) + 1
    by A1,FINSEQ_1:22;
    hence thesis by FINSEQ_1:59,NAT_1:12;
  end;
