anchor.diff:  
   # update the R packages we will need for knitr
   RUN DEBIAN_FRONTEND=noninteractive wget \
  +   https://mirrors.nics.utk.edu/cran/src/contrib/xfun_0.5.tar.gz
      https://mirrors.nics.utk.edu/cran/src/contrib/knitr_1.22.tar.gz \
      https://mirrors.nics.utk.edu/cran/src/contrib/yaml_2.2.0.tar.gz \
      https://mirrors.nics.utk.edu/cran/src/contrib/Rcpp_1.0.1.tar.gz \
  
positive.code:    formatR_1.6.tar.gz \
     evaluate_0.13.tar.gz \
     markdown_0.9.tar.gz \
     knitr_1.22.tar.gz
   
  
  
negative.code:    magrittr_1.5.tar.gz \
     glue_1.3.1.tar.gz \
     stringr_1.4.0.tar.gz \
     xfun_0.5.tar.gz \
     knitr_1.22.tar.gz \
     yaml_2.2.0.tar.gz \
     Rcpp_1.0.1.tar.gz \
  