anchor.diff: -FROM python:3.5-slim-stretch
  +FROM python:3.5-slim-buster
   
   # ensure unoconv can locate the uno library
  -ENV PYTHONPATH=/usr/lib/python3/dist-packages
  +ENV PYTHONPATH /usr/lib/python3/dist-packages
   
   RUN usermod -d /home www-data \
       && chown www-data:www-data /home \
  +    # -slim images strip man dirs, but java won't install unless this dir exists.
  +    && mkdir -p /usr/share/man/man1 \
       && apt-get update \
       # mfr dependencies
       && apt-get install -y \
  
positive.code:     && rm -rf /var/lib/apt/lists/* \
      && pip install -U pip \
      && pip install setuptools==37.0.0 \
      && mkdir -p /code
  
  ENV LIBREOFFICE_VERSION 6.1.6
  ENV LIBREOFFICE_ARCHIVE LibreOffice_6.1.6_Linux_x86-64_deb.tar.gz
  ENV LIBREOFFICE_MIRROR_URL https://download.documentfoundation.org/libreoffice/stable/
  RUN apt-get update \
      && apt-get install -y \
          curl \
          gnupg2 \
      && for server in hkp://ipv4.pool.sks-keyservers.net:80 \
                       hkp://ha.pool.sks-keyservers.net:80 \
                       hkp://pgp.mit.edu:80 \
                       hkp://keyserver.pgp.com:80 \
      ; do \
        gpg --keyserver "$server" --recv-keys AFEEAEA3 && break || echo "Trying new server..." \
      ; done \
      && curl -SL "$LIBREOFFICE_MIRROR_URL/$LIBREOFFICE_VERSION/deb/x86_64/$LIBREOFFICE_ARCHIVE" -o $LIBREOFFICE_ARCHIVE \
          && curl -SL "$LIBREOFFICE_MIRROR_URL/$LIBREOFFICE_VERSION/deb/x86_64/$LIBREOFFICE_ARCHIVE.asc" -o $LIBREOFFICE_ARCHIVE.asc \
          && gpg --verify "$LIBREOFFICE_ARCHIVE.asc" \
          && mkdir /tmp/libreoffice \
          && tar -xvf "$LIBREOFFICE_ARCHIVE" -C /tmp/libreoffice/ --strip-components=1 \
          && dpkg -i /tmp/libreoffice/**/*.deb \
          && rm $LIBREOFFICE_ARCHIVE* \
          && rm -Rf /tmp/libreoffice \
      && apt-get clean \
      && apt-get autoremove -y \
          curl \
          gnupg2 \
      && rm -rf /var/lib/apt/lists/*
  
  RUN pip install unoconv==0.8.2
  
  WORKDIR /code
  
  
negative.code:         freecad \
          # pspp dependencies
          pspp \
          # unoconv dependencies
          libreoffice \
          # gosu dependencies
          curl \
          gnupg2 \
  