public static Range Complete(IList<IFormulaToken> tokens, int index)
{
//var sw = new Stopwatch();
//sw.Start();
// validate input
if (tokens == null || !(0 <= index && index < tokens.Count)) return Range.Empty(0);
// complete token
var instance = new FormulaInterpreter();
var result = instance.Complete2(tokens, index);
//sw.Stop();
// Debug.WriteLine("Interpreter.CompleteToken needed " + sw.ElapsedMilliseconds + "ms");
return result;
}