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Readme.md

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+# PPL Lab Packer
+
+This program packs and encrypts your codes for submission.
+
+More specifically, when you run `pack` in directory `proj`, 
+it will only pack the following files and directories, if they exist.
+
+* files
+  * `proj/dune-project`
+  * `proj/*.opam`
+* directories
+  * `proj/lib`
+  * `proj/bin`
+  * `proj/test`
+
+Such restrictions make uploads slim and without redundant files.
+
+It produces a PGP message `stu-code.pgp.txt`.