Regarding single-letter variables, mathematical functions might be an exception. I think writing func gcd(a, b int) int {...} is better than other alternatives. There is simply no need to assign any more meaning to the arguments other than their type.
Maybe if you - and more importantly, everyone that will read the code in the future - are comfortable with domain-specific expressions like that. It depends on the audience really.
As an extreme example, scalaz is similarly a very specialized DSL. Or in my personal experience, functional constructions like map, flatMap, foldLeft and reduce (which I never learned in school).
For GCD? I would find those names very misleading since semantically the order of the arguments to GCD is irrelevant (even if in the implementation you typically mod by b there's no reason you couldn't mod by a).
