internal static TResult ExecuteSingle<TResult>(IEnumerable<TResult> query, Expression queryRoot)
        {
            return GetElementFunction<TResult>(queryRoot)(query); //①
        }

        private static Func<IEnumerable<TResult>, TResult> GetElementFunction<TResult>(Expression queryRoot)
        {
            SequenceMethod seqMethod;
            if (ReflectionUtil.TryIdentifySequenceMethod(queryRoot, true /*unwrapLambdas*/, out seqMethod))
            {
                switch (seqMethod)
                {
                    case SequenceMethod.First:
                    case SequenceMethod.FirstPredicate:
                        return (sequence) => { return sequence.First(); }; //②

                    case SequenceMethod.FirstOrDefault:
                    case SequenceMethod.FirstOrDefaultPredicate:
                        return (sequence) => { return sequence.FirstOrDefault(); };

                    case SequenceMethod.SingleOrDefault:
                    case SequenceMethod.SingleOrDefaultPredicate:
                        return (sequence) => { return sequence.SingleOrDefault(); };
                }
            }

            return (sequence) => { return sequence.Single(); };
        }

TResult AnonymousMethod(IEnumerable<TResult> sequence)
{
  return sequence.First();
}