I’m not sure I understand the spring example shown. It’s definitely underdetermined as one solution is to have the middle string at tension 0 in which case the

I’m not sure I understand the spring example shown. It’s definitely underdetermined as one solution is to have the middle string at tension 0 in which case there is no difference between what’s shown and what we get when this string is cut. So there seems to be maybe some extra criteria that need to be asserted for when we get the unexpected behavior… but I wonder if when that’s added in explicitly it wouldn’t seem so unintuitive.