On 21b, the Gemara seems to conclude like the din of Rav that אסור להשתמש לאורה. As the בעל המאור writes, this would seem to be a blanket statement that would prohibit all use of the candles whether it is for mitzva or reshus or תשמיש קדושה. The בעל המאור even explains the logic that these candles are a זכר for the menora in the beis hamidkash which are completely אסור בהנאה. Based on this the gemara on 22a א”ר יהודה א”ר אסי אסור להרצות מעות כנגד נר חנוכה would seem to disagree with this din. For this reason, we explained in shiur that this would be the reason to exclude Rav from this din, since it is not in line with the previous statement of Rav that completely negated use of the נרות חנוכה. We then have the following sugya where there is a machlokes if מדליקין מנר לנר. Again, this discussion should not even start according to the original statement of Rav.
However, a problem arises due to the pesak of the Rambam and Rif, who pasken the first sugya like Rav, and yet allow lighting מנר לנר. How can we understand this?
The Ramban defends the Rif and explains that there is another way to understand the case of הרצאת מעות. Rather than understand as we did until now that this is a lower level use than mitzva, he explains that this is a bigger chiddush – since it is just using the candle light for simple glance to see the coins. (in chidushei Haramban he writes that it does not even look like הנאה since it is done from a distance) Therefore, Shmuel who allows הרצאת מעות still agrees with the fundamental din of Rav that אסור להשתמש לאורה and argues about this din since he defines it as הנאה and not תשמיש. This explanation also seems to be peshat of the Rambam as he writes “אסור להשתמש לנר חנוכה … ואפילו לבדוק מעות או למנותן לאורה אסור”
What about הדלקה מנר לנר—why should the Rif and Rambam allow this? The Ramban in the chidushim explains that this is allowed since the two candles are part of the same mitzva and מין במינו אינו בטל. Thus the only תשמיש מצוה allowed is this lighting and one cannot reuse the lights as נרות שבת either as we see in the gemara later.