`z = lambda n:{ x for x in range (2, n+1) if len ([ i for i in range (2, x) if x%i == 0 ]) == 0 }`

I am not sure what functional language this is written in but it seems to be definition of a function which returns a set of prime numbers below the given number. However, I think there is a bug as well (not sure about the language, so I can't be 100% confident). The check in the list should be as following, in my opinion:

`[i for i in range (2, x-1) if x%i == 0]`