Added the mandatory excercise to the repository

aufgaben/src/Pflichtuebung_01/Pu01.elm

@@ -0,0 +1,43 @@
+type alias Day =
+    Int
+
+
+type alias Month =
+    Int
+
+
+type alias Year =
+    Int
+
+
+type alias Date =
+    ( Day, Month, Year )
+
+-- 1 Punkt:
+year : Date -> Year
+--year (a, b, c) = c
+month : Date -> Month
+--month (a,b,c) = b
+day : Date -> Day
+--day (a,b , c) = a
+
+-- 1 Punkt:
+lt : Date -> Date -> Bool
+eq : Date -> Date -> Bool
+gt : Date -> Date -> Bool
+
+-- 1 Punkt:
+toString : Date -> String
+
+-- 2 Punkte:
+next : Date -> Date
+
+-- 2 Punkte:
+prev : Date -> Date
+
+-- 1 Punkt:
+leapyear : Year -> Bool
+
+-- 2 Punkte
+sub : Date -> Date -> Int
+