It means that there was an error in the test suite. Your solution failed, but the failure message is missing, which has been fixed. Try again!

hi,

I'm not entirely sure about what you did, but if your problem is only about the id numbers, don't try to keep track of them, just redefine them when you unlock. See:

The id numbers of the remaining atoms are to be modified so that they are continuous (beginning at 1), keeping the order they had before unlocking the molecule.

if that's not enough, maybe you have troubles about chaining or you're not removing some hydrogens when unlocking?

I ran into the same issue! I belive that the intersection operator does not work because the intersection does not include elements that appear in only one of the key lists.

My solution was to create two new variables - k1 and k2, which were sets of the key lists of c1 and c2 - and use the union of the the two sets.

Therefore, my replacement was k1.union(k2), which creates a new set with elements from both key sets. Note: union is a built-in function that only works for sets.

I hope this is helpful!