static <A> L<A> minus(Collection<A> a, O... b) {
  Set set = asSet(b);
  new L l;
  for (O s : unnull(a))
    if (!set.contains(s))
      l.add(s);
  ret l;
}

static BigInteger minus(BigInteger a, BigInteger b) {
  ret a.subtract(b);
}

ifclass Complex
static Complex minus(Complex c) {
  ret c == null ?: complex(-c.re(), -c.im());
}
endif

meta-for int also as double, long {
  static int minus(int a, int b) {
    ret a-b;
  }
  
  static int minus(int a) {
    ret -a;
  }
}