# The test code:
print map "$_\n", find_gaps(
  qw(2000-4 2000-2 2000-1 2000-12 2001-1 2002-12 1999-12)
);
# The output
2000-3
2000-5
2000-6
2000-7
2000-8
2000-9
2000-10
2000-11
2001-2
2001-3
2001-4
2001-5
2001-6
2001-7
2001-8
2001-9
2001-10
2001-11
2001-12
2002-1
2002-2
2002-3
2002-4
2002-5
2002-6
2002-7
2002-8
2002-9
2002-10
2002-11