@mora You can definitely create variables in a concept. Actually, you can write pretty much what you want in the body of a concept, and the concept will be assigned to a type if substituting for that type makes the body compile. After that, there is no codegen phase, hence you are not **actually** creating a variable - i.e. allocating space - it's only there for the purpose of checking whether something compiles.
About Emmy: it is a little stuck right now, due to [a bug](https://github.com/nim-lang/Nim/issues/3706) in handling `static[T]`, which prevents me to write an efficient implementation of modular arithmetic
