Given: f1, f2 :: Fold Box (HashSet Thing) how do I write a fold that focuses the Things that are in f1 but not in f2? It would (of course) be the same Box, but
mailaddress
windows-forms-designer
semantic-segmentation
microc
gpars
git-fast-import
mosek
python-theano
fcitx
docker-ee
mixture-model
api
stripping
jsblocks
blueimp
lumen-8
mysql-spatial
mingw
wix-extension
permute
bind-variables
tronweb
scalatest-maven-plugin
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webpack-bundle-analyzer
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notorm
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psychtoolbox
jenkins-declarative-pipeline
