opam is missing dependencies

[cogumbreiro]

I tried following the build instructions and found these roadblocks.

$ opam install . --deps-only
...
$ dune build
File "bin/dune", line 5, characters 37-59:
5 |  (libraries disc core bignum sexplib core_unix.command_unix))
                                         ^^^^^^^^^^^^^^^^^^^^^^
Error: Library "core_unix.command_unix" not found.
$ opam install core_unix
$ dune build
File "lib/dune", line 8, characters 61-65:
8 |  (libraries core bignum sexplib core_unix.command_unix oUnit rsdd)
                                                                 ^^^^
Error: Library "rsdd" not found.