private string Apply(RotateByLetter op, string input)
{
int index = input.IndexOf(op.Letter);
int chop = input.Length - (index + 1 + (index >= 4 ? 1 : 0)) % input.Length;
return(input.Substring(chop) + input.Substring(0, chop));
}
private string Apply(RotateByLetter op, string input)
{
Debug.Assert(input.Length == InputLength);
int index = input.IndexOf(op.Letter);
int chop = Unrotate[index];
//int original = index == 0 ? 7 : (index%2 == 0 ? (index + InputLength)/2 - 1 : (index - 1)/2);
return(input.Substring(chop) + input.Substring(0, chop));
}