A-M baby

Task/Five-weekends/PicoLisp/five-weekends.l

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+(setq Lst
+   (make
+      (for Y (range 1900 2100)
+         (for M (range 1 12)
+            (and
+               (date Y M 31)
+               (= "Friday" (day (date Y M 1)))
+               (link (list (get *Mon M) Y)) ) ) ) ) )
+
+(prinl "There are " (length Lst) " months with five weekends:")
+(mapc println (head 5 Lst))
+(prinl "...")
+(mapc println (tail 5 Lst))
+(prinl)
+(setq Lst (diff (range 1900 2100) (uniq (mapcar cadr Lst))))
+(prinl "There are " (length Lst) " years with no five-weekend months:")
+(println Lst)