Rename all the `xs` and `ys` to `as`/`bs` or `fa`/`fb`.
Rename all the `xs` and `ys` to `as`/`bs` or `fa`/`fb`.

Thanks to shaberman on the @typelevel comments for the suggestion.

typelevel/typelevel.github.com,typelevel/typelevel.github.com,melrief/typelevel.github.com,melrief/typelevel.github.com,melrief/typelevel.github.com,S11001001/typelevel.github.com,melrief/typelevel.github.com,S11001001/typelevel.github.com,typelevel/typelevel.github.com,S11001001/typelevel.github.com,S11001001/typelevel.github.com