+ // mockingbird \u.uu = SII
+ constant("M", make_lam(u, make_app(uu, uu)));
+ // warbler \uv.uvv = C(BM(BBT) = C(BS(C(BBI)I))I
+ constant("W", make_lam2(u, v, make_app3(uu, vv, vv)));
+ // lark \uv.u(vv) = CBM = BWB
+ constant("L", make_lam2(u, v, make_app(uu, make_app(vv, vv))));
+ // Y is SLL