Deeper comparison doesn't solve the problem because input order is arbitrary. The order may be based on a user dragging items around in a list widget, for examp

Deeper comparison doesn't solve the problem because input order is arbitrary. The order may be based on a user dragging items around in a list widget, for example. The easiest way to transform an unstable sort into a stable sort is probably mapping input from T -> (Index, T) and including the index as a sort key.