The gemara says that even though Rabbi Shimon does not hold of Muktza he agrees that one can use a big saw and parts of a plow and brings a stam mishna to that effect.
However, a few lines earlier the gemara brought another stam mishnah that disagreed with Rabbi Shimon. How does the Gemara know that the Mishna about the saw is not the opinion of Rabbi Yehudah only?
RASHI (DH Kol ha'Kelim) was bothered by this. He answers that since the Mishnah (which says that the parts of a plow are forbidden) says "*All utensils* may be handled on Shabbos," it implies that even a utensil normally used for a forbidden Melachah (Kli she'Melachto l'Isur) may also be handled on Shabbos. If so, it perforce must be Rabbi Shimon. (Rebbi Shimon argues with Rebbi Yehudah over Kli she'Melachto l'Isur, Shabbos 34b etc. See also the Gemara at the end of 122b, which makes a similar inference from the Mishnah ).