anchor.diff:  
   RUN DEBIAN_FRONTEND=noninteractive R CMD INSTALL \
      jsonlite_0.9.19.tar.gz \
  -   memoise_0.2.1.tar.gz \
  +   memoise_1.0.0.tar.gz \
      whisker_0.3-2.tar.gz \
      RCurl_1.95-4.7.tar.gz \
      Rcpp_0.12.3.tar.gz \
      plyr_1.8.3.tar.gz \
  -   R6_2.1.1.tar.gz \
  -   curl_0.9.4.tar.gz \
  -   httr_1.0.0.tar.gz \
  -   rstudioapi_0.4.0.tar.gz \
  +   R6_2.1.2.tar.gz \
  +   curl_0.9.5.tar.gz \
  +   httr_1.1.0.tar.gz \
  +   rstudioapi_0.45.0.tar.gz \
      brew_1.0-6.tar.gz \
      roxygen2_5.0.1.tar.gz \
      XML_3.98-1.3.tar.gz \
  
positive.code:    http://mirrors.nics.utk.edu/cran/src/contrib/openintro_1.4.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/dplyr_0.4.3.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/assertthat_0.1.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/R6_2.1.1.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/magrittr_1.5.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/lazyeval_0.1.10.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/DBI_0.3.1.tar.gz \
  
negative.code: RUN DEBIAN_FRONTEND=noninteractive R CMD INSTALL \
     openintro_1.4.tar.gz \
     assertthat_0.1.tar.gz \
     R6_2.1.2.tar.gz \
     magrittr_1.5.tar.gz \
     lazyeval_0.1.10.tar.gz \
     DBI_0.3.1.tar.gz \
  