/usr/lib/ghc-doc/hoogle/unlambda.txt is in libghc-unlambda-doc 0.1.3-4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-unlambda-doc/html/unlambda.txt
/usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-unlambda-doc/html/unlambda.txt