anchor.diff:     http://archive.linux.duke.edu/cran/src/contrib/tibble_1.3.3.tar.gz \
      http://archive.linux.duke.edu/cran/src/contrib/dplyr_0.5.0.tar.gz \
      http://archive.linux.duke.edu/cran/src/contrib/assertthat_0.2.0.tar.gz \
  -   http://archive.linux.duke.edu/cran/src/contrib/R6_2.2.1.tar.gz \
  +   http://archive.linux.duke.edu/cran/src/contrib/R6_2.2.2.tar.gz \
      http://archive.linux.duke.edu/cran/src/contrib/magrittr_1.5.tar.gz \
      http://archive.linux.duke.edu/cran/src/contrib/lazyeval_0.2.0.tar.gz \
      http://archive.linux.duke.edu/cran/src/contrib/DBI_0.6-1.tar.gz 
  
positive.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 \
  
negative.code:    http://archive.linux.duke.edu/cran/src/contrib/Archive/roxygen2/roxygen2_5.0.1.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/rversions_1.0.3.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/git2r_0.18.0.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/devtools_1.13.2.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/R6_2.2.2.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/mime_0.5.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/httr_1.2.1.tar.gz \
     http://archive.linux.duke.edu/cran/src/contrib/RCurl_1.95-4.8.tar.gz \
  