Mine

procedure_body Swap_Substring (
	alters Text& t1,
	preserves Integer pos,
	preserves Integer len,
	alters Text& t2
    )
{
    object Integer n = len;
    
    while (n > 0)
    {
	object Character c;
	t1.Remove(pos, c);
	
	n--;
    }

    n = 0;
    while (len_t < t2.Length())
    {
	t1.Add(pos, t2[n]);
    }
}