GEMARA: Rava Said - This is the correct version. The [word] "אלא" is removed.

He did it accidentally: And how to you call it willful?

“If He Came Upon Him Suddenly” This Excludes A [case when someone turns quickly] Around A Corner - The term "suddenly" implies proximity, as the Targum translates it "B'takif" - this excludes a [case when someone turns quickly] around a corner, i.e. if one was exiting from an alley and entering another by turning to the right or to the left, and [he is holding] a knife in his hand, and someone is approaching him from around the corner who he does not see and [therefore] kills.

That he pushed him with his body: without intent.

This includes downward motion that is for a need of upward motion - E.g. one who wants to lift his hand with force while holding an ax, first lowers his body and leans forward so that he [subsequently] be able to lift with strength; and he killed someone while lowering himself. You should not say that since [the downward motion with which he killed] was needed for an upward motion he should be exempt from exile, for [the verse] states "and he cast it [upon him"].

And if one does not lie in wait - He did not intend to throw next to or near him, rather [his intended target was] the location to which he [actually] threw, but he was unaware that there was someone there.

Excludes One Who Intended To Throw Two And Threw Four: And similarly one who [intended to] throw four and threw eight.

So too all [cases] that have permission for the victim etc.: This excludes a privately owned courtyard.

IS THIS [A SITUATION OF] ASCENT OR DESCENT - Do we determine [the law] based on [the direction of] the individual, and he was engaged in an upward motion; or do we determine [the law] based on [the direction of] the rung, and the person ascending upon it was applying pressure as he pushed it downwards?

You've Already Touched Upon it etc. - You are touching upon [the concept] of "descending for the purpose of ascending," which we have already inclusively derived above as [a case where one would be] liable [to a sentence of exile].

This is the correct version: Here is when the [knife is] descending in front of him and ascending behind him. Here is when the upward motion is in front of him but the downward motion is behind him. Here is when the downward motion is both in front of him and behind him. And here is when the upward motion is both in front of him and behind him. Any [incident resulting from an] upward motion is exempt and any [incident resulting from a] downward motion is liable. Therefore, that which was taught "before him, he is liable, behind him is exempt" is referring to [a scenario where] the downward motion was in from of him and the downward motion was behind him, viz. he lowered his arm in order to [then] lift it with force. [So now] when he lifts it with force [if he kills] when lowering in front of him he is liable, [but] if he killed when lifting it behind him he would be exempt. And that which was taught "behind him, he is liable, in front of him, he is exempt" is referring to [a scenario where] the upward motion was in front of him and the downward motion was behind him, e.g. one who lifts his hand with force to the point where it [the ax] was lowered behind him over his shoulders, and then reverses [the motion] to lift [his hands[ to strike in front of him. [So now] if he kills when he was lowering it behind him he is liable, [but if] he killed when he was lifting it [back] he is exempt]. And that which was taught "whether in front of him and behind him, he is liable" is referring to the downward motion, whether it was before him or behind him. And that which was taught "Whether it was in front of him or behind him, he is exempt" is referring to the upward motion, whether it was before or behind him.

Let us say that it is subject to a tannaic dispute: this question of Rebbi Abahu.

Here [one is talking about the issue of] Damages - where he would be obligated to pay the compensation if he did not kill him but only caused him damage. For when it comes to damages there is no difference whether it was caused inadvertently or intentionally, or whether it was done with a downward or upward motion, as we expound in Bava Kamma (26b) [when the verse says] "A laceration for a laceration" [this comes to teach us] that one is obligated for inadvertent damages as [he would be] for intentional damages, and for damages caused beyond his control as [he would be] if they we done willfully.

Here Is When (the rung) Is Rotten - he would be liable [to go to exile] since every rotten rung when it is tread upon it buckles downward, thus constituting a downward motion. But if it is not rotten there is no downward motion.

Here [It] Is [Scenario] When The Rung Has Been Fastened - If the rung completely filled the hole into which it was wedged, and it grasps it very well, then there is no downward motion, and he would thus be exempt [from exile]. If [however] it is not [securely] fastened, then there would be a downward motion, resulting in liability [i.e. exile].

The Transmission Is What Matters - how the word is to be written as it was transmitted to Moses, that is the manner in which we are to expound it, and not the way it pronounced. When you read "V'nashal" you are inserting the pronunciation of a "Aleph" or of a "Hey" between the "Nun" and "Shin", however according to the authoritative tradition it is written as "V'nishal," meaning dislodged, i.e. that the iron caused [a splinter] to become dislodged from the wood [tree] which hit his fellow. Whereas the Rabanan are of the opinion that it the way it pronounced which matters, and it is read "V'nashal" as a verb, i.e. the iron [ax head] itself became dislodged from its wood [handle].