anchor.diff:  RUN DEBIAN_FRONTEND=noninteractive R CMD INSTALL \
      openintro_1.4.tar.gz \
      assertthat_0.1.tar.gz \
  -   R6_2.1.1.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 \
  
positive.code: 
  # R packages we need for devtools - and we need devtools to be able to update the rmarkdown package
  RUN DEBIAN_FRONTEND=noninteractive wget \
     http://mirrors.nics.utk.edu/cran/src/contrib/rstudioapi_0.4.0.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/brew_1.0-6.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/roxygen2_5.0.1.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/rversions_1.0.2.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/git2r_0.13.1.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/devtools_1.9.1.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/R6_2.1.1.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/httr_1.0.0.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/RCurl_1.95-4.7.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/BH_1.60.0-1.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/xml2_0.1.2.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/curl_0.9.4.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/jsonlite_0.9.19.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/downloader_0.4.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/memoise_0.2.1.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/Rcpp_0.12.3.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/plyr_1.8.3.tar.gz \
     http://mirrors.nics.utk.edu/cran/src/contrib/XML_3.98-1.3.tar.gz \
  
negative.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_2.1.2.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 \
  