static void Main()
{
     int i = 3;
     double d = 2.3;
     if (i.In(2, 4, 5).And(d.Between(2.0, 5.3)).Or(i > d))
     MessageBox.Show("Hi!");
}

public static bool In<T>(this T value, params T[] values)
{
     return values.Contains(value);
}

public static bool Between<T>(this T i, T start, T end) where T : IComparable<T>
{
     return i.CompareTo(start) >= 0 && i.CompareTo(end) <= 0;
}

public static bool And(this bool left, bool right)
{
     return left && right;
}

public static bool Or(this bool left, bool right)
{
     return left || right;
}