anchor.diff:  RUN DEBIAN_FRONTEND=noninteractive R CMD INSTALL \
      openintro_1.4.tar.gz \
      assertthat_0.2.0.tar.gz \
  -   R6_2.2.0.tar.gz \
  +   R6_2.2.1.tar.gz \
      magrittr_1.5.tar.gz \
      lazyeval_0.2.0.tar.gz \
      DBI_0.6-1.tar.gz \
  
positive.code:    http://archive.linux.duke.edu/cran/src/contrib/jsonlite_1.4.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/digest_0.6.12.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/downloader_0.4.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/memoise_1.0.0.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/plyr_1.8.4.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/XML_3.98-1.6.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/whisker_0.3-2.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/bitops_1.0-6.tar.gz
  
  RUN DEBIAN_FRONTEND=noninteractive R CMD INSTALL \
     jsonlite_1.4.tar.gz \
     digest_0.6.12.tar.gz \
     memoise_1.0.0.tar.gz \
     whisker_0.3-2.tar.gz \
     bitops_1.0-6.tar.gz \
     RCurl_1.95-4.8.tar.gz \
     Rcpp_0.12.11.tar.gz \
     plyr_1.8.4.tar.gz \
     R6_2.2.0.tar.gz \
     curl_2.4.tar.gz \
     openssl_0.9.6.tar.gz \
     mime_0.5.tar.gz \
  
negative.code: RUN rm \
     openintro_1.4.tar.gz \
     assertthat_0.2.0.tar.gz \
     R6_2.2.1.tar.gz \
     magrittr_1.5.tar.gz \
     lazyeval_0.2.0.tar.gz \
     DBI_0.6-1.tar.gz \
  