I am grateful that a little bit of my own family history is found on this page:
Said R. Cahana b. Tahlifa in the name of R. Cahana b. Minyomi in the name of Rab Cahana b. Malkio who had it from R. Cahana the teacher of Rab [others say that R. Cahana b. Malkio is the same R. Cahana who was Rab's teacher]:
Ok, not really – there are many Cahana’s quoted in the Talmud (usually spelled Kahana or Kahane in English – but all the same in Aramaic!) Who knows who is really related?
But I digress.
We have discussions of interestingly shaped alleyways. For example, one shaped like a centipede – that is a major alleyway with multiple smaller ones running perpendicular off of it, like the legs of a centipede. Except that the opposing mini-alleys cannot be directly across from each other, or they would be considered continuous – they must be staggered. In the instance of that design:
Abaye said: the shape of a doorway is made [at the entrance] of the major alley and all the others are rendered ritually fit by means of a side-post and cross-beam
Another interesting exception is where the terminus of the alley is something other than a wall or door.
It once occurred that one side of an alley terminated in the sea and the other terminated in a rubbish heap, and when the facts were submitted to Rabbi he neither permitted nor forbade [the movement of objects on the Sabbath] in that alley. [He did not declare it] forbidden because partitions in fact existed, [and he did not declare it] permitted since the possibility had to be considered that the rubbish heap might be removed or the sea might recede.
Likewise where a river make a boundary in Sura – nets were raised since there was a possibility of the river receding.
Permanence is important, because people become used to a certain way of doing things and might not recognize when conditions change.
I can relate to that!