EnumerableHelper.cs

namespace example
{
    public static class EnumerableHelper
    {
        public static bool In<T>(this T testValue, params T[] testParameters)
        {
            return testValue.In((left, right) => object.Equals(left, right), testParameters);
        }

        public static bool In<T>(this T testValue, Func<T, T, bool> testFunction, params T[] testParameters)
        {
            foreach (T testParameter in testParameters)
            {
                if (testFunction.Invoke(testValue, testParameter))
                {
                    return true;
                }
            }
            return false;
        }
    }
}