static <A, B> LPair<A, B> filterPairA(Iterable<Pair<A, B>> c, O pred) {
  new LPair<A, B> x;
  if (c != null) for (Pair<A, B> p : c)
    if (p != null && isTrue(callF(pred, p.a)))
      x.add(p);
  ret x;
}

static <A, B, C extends A> LPair<A, B> lambdaMapLike filterPairA(IF1<C, Bool> pred, Iterable<Pair<A, B>> c) {
  ret filterPairA(c, pred);
}

static <A, B, C extends A> LPair<A, B> lambdaMapLike filterPairA(Iterable<Pair<A, B>> c, IF1<C, Bool> pred) {
  ret filterPairA(c, (O) pred);
}