Rabbi Yishmael has a list of 13 ways the Torah's expounded. Why is the Hekesh not included?
1 Answer
This excellent question is asked in Sefer Kritut of Rabbi Shimshon MiKinon, the main book of Klale Hashas. I will copy a couple of statements in English.
First you can see the answer in "ot" "יג" but you need first to read "ot" "יב" .
I think that for you this is sufficient but we need give an English answer. A rough translation of this passage:
In Gemara, Rabbi Akiva and Rabanan have different opinions about the question: "Hekesh is the strongest or Gzera Shava is the strongest?".
... Anyway, we can say that for Rabbi Yishmael Hekehs is the strongest. So all is explained: he doesn't counted the Hekesh because Hekesh is as if the thing is written explicitely {and is not a Drasha}