def execute(self, lf_raw: str) -> int:
        """
        Very basic model for executing friction logical forms. For now returns answer index (or
        -1 if no answer can be concluded)
        """
        # Remove "a:" prefixes from attributes (hack)
        logical_form = re.sub(r"\(a:", r"(", lf_raw)
        parse = semparse_util.lisp_to_nested_expression(logical_form)
        if len(parse) < 2:
            return -1
        if parse[0] == 'infer':
            args = [self._exec_and(arg) for arg in parse[1:]]
            if None in args:
                return -1
            return self._exec_infer(*args)
        return -1