Gershon Dubin comments:
The language in (d) is mashmah that a 4 Amah wall according to the Tana Bara is chayav. This is not so, see Rashi there, since the Tana Bara holds velo ad bichlal, that means chayav from 1,2,3 up to but not including four, which is patur.
Gershon
The Kollel replies:
Yes, you are correct. Sorry for the lack of clarity; we will correct it in our archives, b'Ezrat Hash-m.
Kollel Iyun Hadaf