fn push_both_delimiters<'s>(
entered: &Stack<EnteredDelimiter<'s>>,
lhs_delim: &'s Syntax<'s>,
rhs_delim: &'s Syntax<'s>
) -> Stack<EnteredDelimiter<'s>>
fn push_both_delimiters<'s>(
entered: &Stack<EnteredDelimiter<'s>>,
lhs_delim: &'s Syntax<'s>,
rhs_delim: &'s Syntax<'s>
) -> Stack<EnteredDelimiter<'s>>