static AutoCloseable combineAutoCloseables(final AutoCloseable a, final AutoCloseable b) {
  ret a == null ? b : b == null ? a : autocloseable { a.close(); b.close(); };
}

static AutoCloseable combineAutoCloseables(Iterable<AutoCloseable> l) {
  ret foldl(func(AutoCloseable a, AutoCloseable b) -> AutoCloseable { combineAutoCloseables(a,b) }, l);
}