Thanks!

in what language?

yup, that's a side effect of the last ruby update. Sets were imported automatically, before. Handled.

Looks like there might be an issue with this one with Ruby. I am getting the following error when it gets to the random tests, even after changing my code to a series of if statements returning the answers to the basic tests.

./spec/solution_spec.rb:126:in `block (2 levels) in sol': uninitialized constant Set (NameError)