anchor.diff:  
   # R packages we need for devtools - and we need devtools to be able to update the rmarkdown package
   RUN DEBIAN_FRONTEND=noninteractive wget \
  -   https://archive.linux.duke.edu/cran/src/contrib/processx_3.3.0.tar.gz \
  +   https://archive.linux.duke.edu/cran/src/contrib/processx_3.3.1.tar.gz \
      https://archive.linux.duke.edu/cran/src/contrib/ps_1.3.0.tar.gz \
      https://archive.linux.duke.edu/cran/src/contrib/callr_3.2.0.tar.gz \
      https://archive.linux.duke.edu/cran/src/contrib/crayon_1.3.4.tar.gz \
  
positive.code:    RCurl_1.95-4.12.tar.gz \
     plyr_1.8.4.tar.gz \
     httr_1.4.0.tar.gz \
     sys_3.1.tar.gz \
     askpass_1.1.tar.gz \
     openssl_1.3.tar.gz \
     brew_1.0-6.tar.gz \
     roxygen2_5.0.1.tar.gz \
     BH_1.69.0-1.tar.gz \
     XML_3.98-1.19.tar.gz \
     xml2_1.2.0.tar.gz \
     curl_3.3.tar.gz \
     rversions_1.0.3.tar.gz \
     git2r_0.25.2.tar.gz \
     devtools_2.0.1.tar.gz \
     downloader_0.4.tar.gz
  
  # the CRAN install from source fails because a server at MIT will not respond
  
negative.code:    https://archive.linux.duke.edu/cran/src/contrib/cli_1.1.0.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/desc_1.2.0.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/prettyunits_1.0.2.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/backports_1.1.4.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/rprojroot_1.3-2.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/withr_2.1.2.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/pkgbuild_1.0.3.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/rlang_0.3.4.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/rstudioapi_0.10.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/pkgload_1.0.2.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/rcmdcheck_1.3.3.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/remotes_2.0.4.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/xopen_1.0.0.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/clipr_0.6.0.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/clisymbols_1.2.0.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/sessioninfo_1.1.1.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/usethis_1.5.0.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/sys_3.2.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/askpass_1.1.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/openssl_1.4.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/brew_1.0-6.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/fs_1.3.1.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/gh_1.0.1.tar.gz \
     https://archive.linux.duke.edu/cran/src/contrib/rversions_2.0.0.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_2.0.2.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 \
     https://archive.linux.duke.edu/cran/src/contrib/RCurl_1.95-4.12.tar.gz \
  