oreillymedia/erlang_programming — pull request #2 by derek121 (2014-07-10 17:53:51+00:00)
Title: Fixed deallocate/2 to not add unknown/unallocated frequencies back to Free list

From commit msg:
Changed deallocate/2 to only add Freq back to the list of free frequencies if
it had actually appeared in Allocated. Previously, if a frequency was passed to
deallocate/2 that didn't actually appear in Allocated, it would still be added
into the Free list.