anchor.diff:     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 \
  
positive.code:    formatR_1.6.tar.gz \
     evaluate_0.13.tar.gz \
     markdown_0.9.tar.gz \
     knitr_1.22.tar.gz
   
  
  
negative.code: 
  # 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 \
  