gistfile1.txt

class Whatever
{

    private class StaticBool { public bool Value = false; }

		public RuleBuilder<T0, T1, TR> FirstTimeOnly()
		{
			var fakeStatic = new StaticBool();
			return this.When((P0, P1) =>
			{
				if (fakeStatic.Value) return false;
				fakeStatic.Value = true;
				return true;
			});
		}
}