The chain would start: Box - J - Lid Maria adds hers: Box - J - Lid | M Jan can open his padlock, releasing hers, and transfo

The chain would start: Box - J - Lid Maria adds hers: Box - J - Lid | M Jan can open his padlock, releasing hers, and transform this to: Box - J - M - J - Lid Which Maria can open. An optimization could be: Box - M - J - Lid This is available if Maria could fit her padlock through the port in the box simultaneously with Jan's there, and send that back so Jan could remove his initial box padlock. And the arrangement Box - M - J - Lid | | J M Would let either start a new box, using the J - M - J or M - J - M chaining as needed.