Lets say we have a language where each function can return a string expression of itself. E.g. print.str() = "print". gen_exp() uses this function at least for some of its operation. Once we transpile the resulting expression will no longer run in the target language, even with the inner call to transpile. Maybe there is an easy solution to this issue too, but it seems I can keep coming up with new complications the transpiler will need to account for, thus I can't see how transpilation can be guaranteed in general. We would need a general proof that no counter example is ever possible for some given transpilation scheme to guarantee generality.