reserve D for non empty set,
  f for FinSequence of D,
  p, p1, p2, p3, q for Element of D,
  i, j, k, l, n for Nat;

theorem
  1 <= i & i < len f implies Swap(f, i, len f) = (f|(i-'1))^<*f/.len f*>
  ^((f/^i)|(len f-'i-'1))^<*f/.i*>
proof
  assume 1 <= i & i < len f;
  then
  Swap(f,i,len f) = (f|(i-'1))^<*f/.len f*>^(f/^i)|(len f-'i-'1)^<*f/.i*>^
  (f/^len f) by Th27
    .= (f|(i-'1))^<*f/.len f*>^(f/^i)|(len f-'i-'1)^<*f/.i*>^{} by RFINSEQ:27;
  hence thesis by FINSEQ_1:34;
end;
