towards better error handling: all MTerms are annotated with positions, so we can reconstruct the text of a mterm and its context. When error happens and wrong mterm is identified, we show this mterm (in the context!) in red in console. This is done for all errors except typing. The next step for typing errors: during type checking, we should record a path to the term, so when a sub-term is not a well-typed, having this path, we can reconstruct corresponding MTerm.