Function seq2 

pub fn seq2<'arn, 'grm: 'arn, 'a, O1, O2, E: ParseError>(
    p1: &'a impl Parser<'arn, 'grm, O1, E>,
    p2: &'a impl Parser<'arn, 'grm, O2, E>,
) -> impl Parser<'arn, 'grm, (O1, O2), E> + 'a