{"ast_node_type":"variable","tokens":[{"end":73,"kind":"keyword","start":0,"text":"let"}]}
                let principal = |tty: &Binders<QuantifiedWhereClauses>| {
            (Some(PointerKind::VTable(src_tty)), Some(PointerKind::VTable(dst_tty))) => {
                    tty.skip_binders().as_slice(Interner).first().and_then(|pred| {