This function will be called on nodes of a logical form tree, which are either non-terminal
        symbols that can be expanded or terminal symbols that must be leaf nodes.  Returns ``True``
        if the given symbol is a terminal symbol.

def is_terminal(self, symbol: str) -> bool:
        """
        This function will be called on nodes of a logical form tree, which are either non-terminal
        symbols that can be expanded or terminal symbols that must be leaf nodes.  Returns ``True``
        if the given symbol is a terminal symbol.
        """
        # We special-case 'lambda' here because it behaves weirdly in action sequences.
        return (symbol in self.global_name_mapping or
                symbol in self.local_name_mapping or
                'lambda' in symbol)