R' Tarfon suggests two kal vachomers in the mishna. One is that we see from Shein V'regel that reshus hanizik is more chamur than reshus harabim, so if keren is chayav half in reshus harabim, it should surely be chayev full in reshus hanizik. The other one is that we see by reshus harabim that keren is more chamur than Shein V'regel. So if Shein V'regel are chayev full in reshus hanizik, keren will surely be chayev full in reshus hanizik. The Rabbanan respond that both kal vachomers are invalid because of Dayo. The Dayo in the first kal vachomer is logical because the fact that reshus hanizik is more chamor than reshus harabim doesn't prove that the payment will be more. It only proves that the payment can't be less. But the dayo in the second kal vachomer is illogical, because if keren is more chamor than Shein V'regel which pay full, there is no way that keren can pay less than full. The Gemara asks how R' Tarfon can disagree with this considering that Dayo is learned out f

rom a pasuk in the Torah. What's the Gemara's question? The pasuk is only discussing a kal vachomer which is parallel to R' Tarfon's first kal vachomer (where Dayo is logical). But the Gemara never brings a pasuk that shows that we also say Dayo in a case like R' Tarfon's second kal vachomer (i.e. where it's illogical).

Tzvi Hertzberg, Flushing, New York