pub fn super_lattice_tys<'a, 'tcx, L>( this: &mut L, a: &'tcx TyS<'tcx>, b: &'tcx TyS<'tcx>) -> Result<&'tcx TyS<'tcx>, TypeError<'tcx>> where 'tcx: 'a, L: LatticeDir<'a, 'tcx>,