[Disks intersection] Same radius validator fails!?

Concerning the community puzzle “Disks intersection”: My problem is that the validator (which ofc. differs from test case) for “Same Radius” fails on my solution. No I didn’t hardcode it. It passes all other test cases and validators.

My solution is based on the formula easily found on the web, I use python3 and the default math package. I tried two different approaches to see if some subtractions lead to rounding errors. I tried handling the special case when the radi are exactly equal. I tried to handformat the output value. No luck.
What is the problem with this validator?

Beware, you can’t use the formula without using your brain for some test cases.

Ok I got it, I was on the wrong track because of the validator’s name and searched for errors in the formula.
I already handled the special cases separately but got the radi switched up at one point. Thanks