/// <summary>
/// Check argument and throw instantiation exception if necessary.
/// </summary>
public static void Check(object task, object arg, bool shouldBeInstantiated, BindingEnvironment e,
object[] args)
{
if (!(e.Resolve(arg) is LogicVariable) != shouldBeInstantiated)
{
throw new ArgumentInstantiationException(task, e, args);
}
}