With Rosh Chodesh Kislev approaching, Chanukah is on the way. There is a famous machlokes [dispute] in the Gemara (Maseches Shabbos) on the following question: Madlikin mi’ner l’ner, o lo? (Can you take a Chanukah candle and use it to light another Chanukah candle? Yes or no?) On this there is a machlokes [between] Rav and Shmuel: Rav says no, Shmuel says yes. Rav says no because ka mach’chish mitzvah – you diminish the mitzvah. If I take a light to light another light, then I’m going to spill a little of the oil, or a little of the wax and the result is that I will diminish the first light. And Shmuel doesn’t worry about this. Now, we know, in general, Machlokes Rav u’Shmuel, halachah k’Rav – the law is always according to Rav (against Shmuel) with only three exceptions, and this is one of them.