def nth_wday_in_month(n, which_wday)
first_of_month = change(:day => 1)
first_in_month = first_of_month.advance(:days => (which_wday - first_of_month.wday))
first_in_month = first_in_month.advance(:days => 7) if first_in_month.month != first_of_month.month
if n > 0
first_in_month.advance(:days => (7*(n - 1)))
else
possible = first_in_month.advance(:days => 21)
possible = possible.advance(:days => 7) while possible.month == first_in_month.month
last_in_month = possible.advance(:days => - 7)
(last_in_month.advance(:days => - (7*(n.abs - 1))))
end
end