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!

why

respect for the dedication