we bring a rayoh to show that we don't do kasher zomam and make the aidim zomimin chalolim because the posuk says lo'h and we learn out from here lo'h velo'h lezaroh.
Q. why is this clear rayoh from the posuk not good enough and the gemorah trys to bring a rayoh from a kal vechomer and only when that was proven wrong the gemorah settles with the original answer?
daniel, london
The Ritva gives two possibilities as to why Bar Pada brought his Kal v'Chomer. It is possible that Bar Pada in fact agrees with the previous answer, and merely thought to bring a proof to it through a Kal v'Chomer. On the other hand, the Ritva says, it is also possible that Bar Pada rejects the teaching from "Lo," thinking that it would still be considered "Ka'asher Zamam" if the witnesses themselves would become Chalalim.
All the best,
Yaakov Montrose