anchor.diff:      add-apt-repository 'deb http://cran.rstudio.com/bin/linux/ubuntu trusty/' && \
       add-apt-repository ppa:git-core/ppa && \
       add-apt-repository ppa:pi-rho/dev && \
  -    apt-key adv --keyserver keyserver.ubuntu.com --recv-keys E084DAB9 &&
  +    apt-key adv --keyserver keyserver.ubuntu.com --recv-keys E084DAB9 && \
       apt-get update && apt-get install -y -q curl && \
       (curl -sL https://deb.nodesource.com/setup_4.x | sudo -E bash -)
   
  
positive.code: 
  # Install Emacs 24.5 from source.
  
  RUN wget http://ftp.gnu.org/gnu/emacs/emacs-24.5.tar.gz &&
      tar xzf emacs-24.5.tar.gz &&
      (cd /tmp/build/emacs-24.5 && ./configure && make && make install)
  
  # Install Python 2.7.11.
  
  RUN apt-get update -y && apt-get install -y libffi-dev libffi6 libffi6-dbg &&
      wget https://s3-us-west-1.amazonaws.com/royseto-public/dpkg/python2.7.11_2.7.11-local1_amd64.deb &&
      dpkg -i python2.7.11_2.7.11-local1_amd64.deb
  
  # Enable passwordless sudo for users in the sudo group.
  
negative.code: 
  WORKDIR /
  RUN /bin/rm -rf /tmp/build
  