{"ast_node_type":"variable","tokens":[{"end":70,"kind":"keyword","start":0,"text":"let"}]}
    let invariant = terms_cx.arena.alloc(ConstantTerm(ty::Invariant));
    let contravariant = terms_cx.arena.alloc(ConstantTerm(ty::Contravariant));
    let bivariant = terms_cx.arena.alloc(ConstantTerm(ty::Bivariant));