anchor.diff:      iterators_1.0.10.tar.gz \
       listenv_0.7.0.tar.gz \
       tidyverse_1.2.1.tar.gz \
  -    promises_1.0.1.tar.fs_1.2.7.tar.gz    future_1.9.0.tar.gz \
  +    promises_1.0.1.tar.
  +    future_1.9.0.tar.gz \
       doMC_1.3.5.tar.gz \
       foreach_1.4.4.tar.gz \
       doParallel_1.0.11.tar.gz \
  
positive.code:    https://archive.linux.duke.edu/cran/src/contrib/brew_1.0-6.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/magrittr_1.5.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/Archive/roxygen2/roxygen2_5.0.1.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/rversions_1.0.3.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/git2r_0.25.2.tar.gz \
     
     https://archive.linux.duke.edu/cran/src/contrib/devtools_2.0.1.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/R6_2.4.0.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/httr_1.4.0.tar.gz \
  
negative.code:    wget \
     sudo \
     libcurl4-openssl-dev \
     libxml2-dev \
     libgit2-dev
  
  # we need TeX for the rmarkdown package in RStudio, and pandoc is also useful 
  RUN apt-get update 
  