Reish Lakish says that if you combine pigul, nosar and tameh the 3 become batal and if a person eats them, he is not lokeh.
I understand that one way of looking at this is because of hasra'as safek. It seems though, that tosefas tries to explain how they can become batal. But I do not understand how the different issurs can cancel each other. I did not really understand the argument tosefos gave. To me it seems quite a bit different than milk in meat etc., since in my understanding here one has equal amounts (a kezais) of each issur, he just eats them all one time. Moreover in tosefos' girsa, there is only 2 minim, not 3 (which according ot the gilyon agrees with the yerusahlmi's girsah -- see below).
I came to this sugya through Mesechas Chala daf 2b in the yerushalmi. The gemmarah quotes Reish Lakish, as recorded in Zevachim with tosefos' girsa. The gemarrah in Challah then quotes R'Yochanan who states that if one (as Hillel did) combines (Koreich) a kezais each of matzah, marror and the karbon pesach and eats them together one is NOT yotzeh any of these 3 miztvahs as they all cancel each other out. Certainly given this, the yerushalmi does not see hasraas safek as the issue in the absence of makkos, but as a bitul issue. In trying to undrstand this, I looked up the case in Zevachim and did not get a good understanding of the discussion there either.
martin fogel, carlsbad, ca
Rashi explains that when a person eats the two (or more) Isurim together, as he chews both at the same time, in each mouthful there will be slightly more of one than the other, and therefore one will be Batel in the other. Rashi is of the opinion that the one that is Batel acquires the Dinim of the one that was Mevatel it, and hence he has certainly eaten a k'Zayis of Isur but we do not know which Isur was Mevatel the other. Therefore, even though he has certainly eaten a Shi'ur of Isur, even if he had Hasra'ah he cannot get Malkos, because we did not know at the time of the Hasra'ah that if he would do the act we are warning him not to do, that he would thus be transgressing the Isur we are warning him from. This is true even if he ate two Zeisim (one each of two Isurim) and we warned him before each one for the same Isur, in such a way that we now know that he certainly transgressed the Isur we warned him about at one stage.
Tosfos in their second Pshat offer a similar explanation to Rashi as far as the Bitul is concerned. In their first Pshat they explain that the Gemara is talking about two pieces, each one consisting of three Zeisim, one with two Zeisim of Pigul and one of Nosar, and the second with two of Nosar and one of Pigul. Here the Bitul takes place in each individual piece, since each piece has Rov of one Isur. Here also, he ate both pieces and received Hasra'ah before each eating for the same Isur.
Although Tosfos does not mention Tamei in the Dibur ha'Maschil, they do mention that there are three Isurim in the Sugya. See Rashash and Olas Shlomoh who discuss this point.