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_1.12.tar.gz \
  +   http://mirrors.nics.utk.edu/cran/src/contrib/knitr_1.12.3.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_0.3.tar.gz \
      http://mirrors.nics.utk.edu/cran/src/contrib/caTools_1.17.1.tar.gz \
  
positive.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 \
  
negative.code:    stringi_1.0-1.tar.gz \
     magrittr_1.5.tar.gz \
     stringr_1.0.0.tar.gz \
     knitr_1.12.3.tar.gz \
     yaml_2.1.13.tar.gz \
     htmltools_0.3.tar.gz \
     caTools_1.17.1.tar.gz \
  