/// <summary>
/// Rotate the collection to the left so that the item at startIndex becomes index 0.
/// Elements rotated to the left wrap around, so the number of elements stays the same.
/// </summary>
public static System.Collections.Generic.IEnumerable <T> Rotate <T>(this System.Collections.Generic.ICollection <T> targets, int startIndex)
{
return(targets.Skip(startIndex).Concat(targets.Take(startIndex)));
}