anchor.diff:  
   # update the R packages we will need for knitr
   RUN DEBIAN_FRONTEND=noninteractive wget \
  -   http://mirrors.nics.utk.edu/cran/src/contrib/knitr_1.11.tar.gz \
  +   http://mirrors.nics.utk.edu/cran/src/contrib/knitr_1.12.tar.gz \
      http://mirrors.nics.utk.edu/cran/src/contrib/yaml_2.1.13.tar.gz \
  -   http://mirrors.nics.utk.edu/cran/src/contrib/htmltools_0.2.6.tar.gz \
  +   http://mirrors.nics.utk.edu/cran/src/contrib/htmltools_0.3.tar.gz \
      http://mirrors.nics.utk.edu/cran/src/contrib/caTools_1.17.1.tar.gz \
      http://mirrors.nics.utk.edu/cran/src/contrib/bitops_1.0-6.tar.gz \
  -   http://mirrors.nics.utk.edu/cran/src/contrib/digest_0.6.8.tar.gz \
  +   http://mirrors.nics.utk.edu/cran/src/contrib/digest_0.6.9.tar.gz \
      http://mirrors.nics.utk.edu/cran/src/contrib/stringr_1.0.0.tar.gz \
      http://mirrors.nics.utk.edu/cran/src/contrib/markdown_0.7.7.tar.gz \
      http://mirrors.nics.utk.edu/cran/src/contrib/highr_0.5.1.tar.gz \
  
positive.code: # mccahill/r-studio
  #
  # VERSION               0.7.2
  
  FROM   ubuntu:14.04
  MAINTAINER Mark McCahill "mark.mccahill@duke.edu"
  
negative.code:    formatR_1.2.1.tar.gz \
     evaluate_0.8.tar.gz \
     markdown_0.7.7.tar.gz \
     knitr_1.12.tar.gz 
  
  RUN rm \
     evaluate_0.8.tar.gz \
  