both First and Follow are equivalent to vec![BitSet(g.token_num()); g.nt.len()] (calculating the first/follow set of terminal is meaningless)

terminal id is distributed in [0, terms.len()) non-terminal id is distributed in [terms.len(), terms.len() + nt.len()) there are 3 fixed terminal id:

first set and ps set are useless for parser generating, if you need them, `LLCtx::new` have these 2 local variables update: now first set is added bac

originally the `link` field type is a generic parameter L: Borrow<Link> because the Lr1Node generated from `lalr1_by_lr0` is a borrowed ref of the `li