(Mishnah): If Reuven said 'it is Alai to bring the Korbanos of a half-Nazir', and Shimon heard this and said 'also I, it is Alai to bring the Korbanos of a half-Nazir', each must bring Korbanos of a full Nazir. R. Meir says so;

Chachamim say, each brings the Korbanos of a half-Nazir.

(Gemara - R. Avahu citing R. Yochanan, and Rav Chisda): They argue in a Stam case (this will be explained).

Question: What is the case?

If he said 'half the head' (i.e. he will bring the obligation of a half-Nazir), all agree that he is Megale'ach a full Nazir;

If he said 'half the obligation, all agree that he is Megale'ach half a Nazir!

Answer: The case is, he said 'half'. R. Meir says, it is as if he said 'half the head.' Rabanan say, it is as if he said 'half the obligation.'

(R. Yudan): We find a leniency and stringency in R. Meir's opinion, who says 'half the head.' He brings one Korban, for a Nazir may shave on it, according to R. Shimon (Mishnah 6:10). According to Rabanan, who say 'half the obligation', he brings (pays for) one and a half Korbanos, which is half an individual's obligation. (We explained this like NO'AM YERUSHALMI. According to Rabanan (below, 4:5) who say that he may not drink until bringing all three Korbanos, R. Meir is more stringent; he requires bringing all three.)