assert that angdiff($a,$b) must be ..."

But there's a rub. It's that pesky "..." part.

##</code><code>##

"so that's as far apart...." 

##</code><code>##

"so that's the farthest apart...."

##</code><code>##

because even though they have a 0% frequency, the fact that the show up in the list at all means they were tested at least once.