Tos. is wondering how the sugia of zirza dekanei fits in with the gemora here. Tos. explains that this case is similar to omed lekatef, in other words, that a hanacha that is done as a necessary and normal part of an action is not considered a hanacha. Since the gemora was now discussing an amud of 9, that is rabim mechatfim alav therefore the gemorah discusses the zirza dekanei that also has to do with omed lekatef. Is this just a play on words? Seemingly the concept of an amud being part of the reshus harabim because it is used for katef purposes is unrelated to the concept of omed lekatef not being considered a hanacha.
Mordechai Fine - email@example.com
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The connection between this Gemara and the previous Sugya, as Tosfos explains it, is not based on play on words. Rather, the the Gemara here is an actual application of the principle introduced earlier, as you mentioned in your question. The act which people do upon an Amud in Reshus ha'Rabim -- placing their loads upon it in order to re-arrange it on their shoulders -- is not considered a Hanachah and therefore one who did such an act after walking two Amos and then continues walking another two Amos is Chayav. We might have assumed, based on this principle, that one who is pushing a bundle of sticks in Reshus ha'Rabim will also be Chayav after walking four Amos, even though there was a Hanachah after each Amah, because those Hanachos do not count as such. Therefore, Rav Yehudah had to explicitly teach that one will be Patur, because those Hanachos do count in the case of shlepping bundles of sticks.