You're rigorous as usual ikegami, your realname wouldn't be Spock? ;)

My point is that a simple algorithm could be used instead of importing a module, but I should have specified it's parameters more thoroughly:

# positive integer, current year 
my $year = 

# integer 1 to 12, current month
my $month = 

# positive integer, number of months to go back
my $monthsback =
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