Coq translation. I changed rationals to reals because it is more convenient to work with real numbers in Coq (and also arctan is a real-valued function).

As others have pointed out, the assertions are broken. You can either fix it by running abs/1 on the difference between expected and actual, or, better yet, ditch your home made assertion and use ExUnit's assert_in_delta.

This kata is broken. You can return anything.

The assert statement is completely wrong, returning any number pass the tests.

• Needs Random Test
• The lower of the sum in given formula should be k=1 instead of k=0