Displayable, and multiplication-composable etc., functions on vector space using the  newtype from Data.Monoid. This might not be necassary,  could suffice.
Function definitions work. Not really flexible or beautiful yet.
Functions now render quite properly, with considerable render-configuration options.
Made 'mathFuncDefinition' Rank3-polymorphic, so the argument can also be used in e.g. sums.
Value- or function definitions can also work when there are free variables in scope / argument-stack closure.
Made the rendering monad parametric on the stack/closure of free variables. This paves a way for safely introducing such variables at any point of a proof.