anchor.diff:  
   # Install RVM, Ruby, and gist.
   
  -RUN gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3 &&
  -    (curl -sSL https://get.rvm.io | bash -s stable --ruby) &&
  +RUN gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3 && \
  +    (curl -sSL https://get.rvm.io | bash -s stable --ruby) && \
       bash -c "(. /usr/local/rvm/scripts/rvm && gem install gist)"
   
   # Install npm packages.
  
positive.code: 
  WORKDIR /
  RUN /bin/rm -rf /tmp/build
  
  
  
negative.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.
  