reserve i,j,k,n,m for Nat,
  x,y,z,y1,y2 for object, X,Y,D for set,
  p,q for XFinSequence;

theorem Th12: ::FINSEQ_5:40
  (p^q)/^(len p) = q
proof
  thus (p^q)/^(len p) = (p^q)/^(len p + (0 qua Element of NAT))
    .= q/^0 by Th11
    .= q by Th10;
end;
