-keep-hc-files or -keep-hc-file?

I'm currently confused if it must be plural or singular (or any) http://www.haskell.org/ghc/docs/latest/html/users_guide/separate-compilation... shows plural options whereas http://www.haskell.org/ghc/docs/latest/html/users_guide/flag-reference.html#... shows them in singular (except -keep-tmp-files) Cheers Christian