My stackoverflow answer on: Check if string is a rotation of other string

Found a curious puzzle on stackoverflow, how to check if the string is a rotation of another string.

My provided answer uses the modulo approach.  Hats off to the voted answer(uses concatenation approach), it's the best, I think even Jon Skeet was impressed :-)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace IsRotation
{
class Program
{
    static void Main(string[] args)
    {
        
        Console.WriteLine("Rotation : {0}", 
            IsRotation("stackoverflow", "ztackoverflow"));


        Console.WriteLine("Rotation : {0}", 
            IsRotation("stackoverflow", "ackoverflowst"));

                
        
        Console.WriteLine("Rotation : {0}", 
            IsRotation("stackoverflow", "overflowstack"));
        Console.WriteLine("Rotation : {0}", 
            IsRotation("stackoverflow", "stackoverflwo"));

        Console.WriteLine("Rotation : {0}",
                IsRotation("stackoverflow", "owstackoverfl"));


        string strToTestFrom = "stackoverflow";
        foreach(string s in StringRotations(strToTestFrom))
        {
            Console.WriteLine("is {0} rotation of {1} ? {2}", 
                s, strToTestFrom,
                IsRotation(strToTestFrom, s) );
        }


        Console.ReadLine();
    }

    public static IEnumerable StringRotations(string src)
    {            
        for (int i = 0; i < src.Length; ++i)
        {
            var sb = new StringBuilder();
            for (int x = 0; x < src.Length; ++x)
                sb.Append(src[(i + x) % src.Length]);

            yield return sb.ToString();
        }
    }


    public static bool IsRotation(string a, string b)
    {           
        if (b.Length != a.Length || a.IndexOf(b[0]) < 0 ) return false;
        foreach(int ndx in IndexList(a, b[0]))
        {
            int i = ndx;
            if (b.ToCharArray().All(x => x == a[i++ % a.Length])) 
                return true;
        }
        return false;
    }

    public static IEnumerable<int> IndexList(string src, char c)
    {
        for (int i = 0; i < src.Length; ++i)
            if (src[i] == c)
                yield return i;
    }

}//class Program
}//namespace IsRotation

Output:

Rotation : False
Rotation : True
Rotation : True
Rotation : False
Rotation : True
is stackoverflow rotation of stackoverflow ? True
is tackoverflows rotation of stackoverflow ? True
is ackoverflowst rotation of stackoverflow ? True
is ckoverflowsta rotation of stackoverflow ? True
is koverflowstac rotation of stackoverflow ? True
is overflowstack rotation of stackoverflow ? True
is verflowstacko rotation of stackoverflow ? True
is erflowstackov rotation of stackoverflow ? True
is rflowstackove rotation of stackoverflow ? True
is flowstackover rotation of stackoverflow ? True
is lowstackoverf rotation of stackoverflow ? True
is owstackoverfl rotation of stackoverflow ? True
is wstackoverflo rotation of stackoverflow ? True

The accepted answer(hint already included in the question itself) is kinda cool, it concatenates the source string to itself, all the possible rotation is inside the concatenated string.