public static MethodInfo SelectMany_Index_TSource_TResult_2(Type TSource, Type TResult) =>
(s_SelectMany_Index_TSource_TResult_2 ??
(s_SelectMany_Index_TSource_TResult_2 = new Func<IQueryable<object>, Expression<Func<object, int, IEnumerable<object>>>, IQueryable<object>>(Queryable.SelectMany).GetMethodInfo().GetGenericMethodDefinition()))
.MakeGenericMethod(TSource, TResult);