public static bool Keep(List<Foo> foos, Foo foo, string argumentBar)
{
  bool flag = false;
  foreach (var oldFoo in foos)
  {
    if (oldFoo.OldStuff.Baz == foo.Baz)
    {
      if (oldFoo.Xyzzy == MyBoringEnum.SomeValue)
      {
        if (argumentBar == "f00")
        {
          flag = true;
        }
      }
    }
  }
  return flag;
}