static <A, B, C, D> T3<A, D, C> tripleMapB(T3<A, B, C> t, IF1<B, D> f) {
  ret t == null ? null : triple(t.a, f.get(t.b), t.c);
}

static <A, B, C, D> T3<A, D, C> lambdaMapLike tripleMapB(IF1<B, D> f, T3<A, B, C> t) {
  ret tripleMapB(t, f);
}