Slice<T>(int start, int end)

public static IEnumerable<T> Slice<T>(this IEnumerable<T> collection, int start, int end)
{
    int index = 0;
    int count = 0;

    if (collection == null)
        throw new ArgumentNullException("collection");

    // Optimise item count for ICollection interfaces.
    if (collection is ICollection<T>)
        count = ((ICollection<T>)collection).Count;
    else if (collection is ICollection)
        count = ((ICollection)collection).Count;
    else
        count = collection.Count();

    // Get start/end indexes, negative numbers start at the end of the collection.
    if (start < 0)
        start += count;

    if (end < 0)
        end += count;

    foreach (var item in collection)
    {
        if (index >= end)
        yield break;

        if (index >= start)
        yield return item;

        ++index;
    }
}

char[] h = "0123456789abcdef".ToCharArray();

var a = h.Slice(0, 3);    // returns { 0, 1, 2 }
var b = h.Slice(4, 9);    // returns { 4, 5, 6, 7, 8 }
var c = h.Slice(10, 100); // returns { a, b, c, d, e, f }
var d = h.Slice(5, 5);    // returns { }
var e = h.Slice(-10, -5); // returns { 6, 7, 8, 9, a }