diff --git a/code/Angabe4.lhs b/code/Angabe4.lhs
index dcdf41e..a4ec56c 100644
--- a/code/Angabe4.lhs
+++ b/code/Angabe4.lhs
@@ -92,6 +92,102 @@ Helper functions:
 > month_to_str Nov = "11"
 > month_to_str Dez = "12"
 
+> day_to_int :: Tag -> Int
+> day_to_int I = 1
+> day_to_int II = 2
+> day_to_int III = 3
+> day_to_int IV = 4
+> day_to_int V = 5
+> day_to_int VI = 6
+> day_to_int VII = 7
+> day_to_int VIII = 8
+> day_to_int IX = 9
+> day_to_int X = 10
+> day_to_int XI = 11
+> day_to_int XII = 12
+> day_to_int XIII = 13
+> day_to_int XIV = 14
+> day_to_int XV = 15
+> day_to_int XVI = 16
+> day_to_int XVII = 17
+> day_to_int XVIII = 18
+> day_to_int XIX = 19
+> day_to_int XX = 20
+> day_to_int XXI = 21
+> day_to_int XXII = 22
+> day_to_int XXIII = 23
+> day_to_int XXIV = 24
+> day_to_int XXV = 25
+> day_to_int XXVI = 26
+> day_to_int XXVII = 27
+> day_to_int XXVIII = 28
+> day_to_int XXIX = 29
+> day_to_int XXX = 30
+> day_to_int XXXI = 31
+> day_to_int _ = 100
+
+> month_to_int :: Monat -> Int
+> month_to_int Jan = 1
+> month_to_int Feb = 2
+> month_to_int Mar = 3
+> month_to_int Apr = 4
+> month_to_int Mai = 5
+> month_to_int Jun = 6
+> month_to_int Jul = 7
+> month_to_int Aug = 8
+> month_to_int Sep = 9
+> month_to_int Okt = 10
+> month_to_int Nov = 11
+> month_to_int Dez = 12
+> month_to_int _ = 100
+
+> int_to_day :: Int -> Tag
+> int_to_day 1 = I
+> int_to_day 2 = II
+> int_to_day 3 = III
+> int_to_day 4 = IV
+> int_to_day 5 = V
+> int_to_day 6 = VI
+> int_to_day 7 = VII
+> int_to_day 8 = VIII
+> int_to_day 9 = IX
+> int_to_day 10 = X
+> int_to_day 11 = XI
+> int_to_day 12 = XII
+> int_to_day 13 = XIII
+> int_to_day 14 = XIV
+> int_to_day 15 = XV
+> int_to_day 16 = XVI
+> int_to_day 17 = XVII
+> int_to_day 18 = XVIII
+> int_to_day 19 = XIX
+> int_to_day 20 = XX
+> int_to_day 21 = XXI
+> int_to_day 22 = XXII
+> int_to_day 23 = XXIII
+> int_to_day 24 = XXIV
+> int_to_day 25 = XXV
+> int_to_day 26 = XXVI
+> int_to_day 27 = XXVII
+> int_to_day 28 = XXVIII
+> int_to_day 29 = XXIX
+> int_to_day 30 = XXX
+> int_to_day 31 = XXXI
+
+> int_to_month :: Int -> Monat
+> int_to_month 1 = Jan
+> int_to_month 2 = Feb
+> int_to_month 3 = Mar
+> int_to_month 4 = Apr
+> int_to_month 5 = Mai
+> int_to_month 6 = Jun
+> int_to_month 7 = Jul
+> int_to_month 8 = Aug
+> int_to_month 9 = Sep
+> int_to_month 10 = Okt
+> int_to_month 11 = Nov
+> int_to_month 12 = Dez
+
 > skonto_to_num :: Skonto -> Float
 > skonto_to_num s
 >   | s == KeinSkonto = 0
@@ -107,13 +203,13 @@ Helper functions:
 >   | monat d == Feb =
 >      let y = jahr d in
 >      let t = tag d in
->         if y `mod` 4 /= 0 && (day_to_str t) > (day_to_str XXVIII) then False
+>         if y `mod` 4 /= 0 && (day_to_int t) > 28 then False
 >         else
 >            if y `mod` 100 == 0 && y `mod` 400 /= 0 then False
 >            else
->               if (day_to_str t) > (day_to_str XXIX) then False
+>               if (day_to_int t) > 29 then False
 >               else True
->   | (day_to_str (tag d)) > (day_to_str XXX) && not(monat d `elem` full_months) = False
+>   | (day_to_int (tag d)) > 30 && not(monat d `elem` full_months) = False
 >   | otherwise = True
 
 > is_payment :: Geschaeftsvorfall -> Bool
@@ -128,6 +224,7 @@ Helper functions:
 >      Gutschrift _ _ -> True
 >      _ -> False
 
+
 Aufgabe A.1
 
 > type P_Geschaeftspartner = Geschaeftspartner
@@ -140,9 +237,11 @@ Aufgabe A.1
 >                    } deriving (Eq,Show)
 > type AP_Kassabucheintrag = (P_Geschaeftspartner,AP_Geschaeftsvorfall)
 
+
 > waup :: Kassabucheintrag -> AP_Kassabucheintrag
 > waup (g, v) = eval_payment_sum $ eval_payment_date (g, v)
 
+
 > eval_payment_date :: Kassabucheintrag -> Kassabucheintrag
 > eval_payment_date (g, v)
 >   | (is_payment v) && (is_date_valid (zahlung_vom v)) =
@@ -159,11 +258,31 @@ Aufgabe A.1
 >       z = Zahlung (brutto v) (skonto v) (correct_date (zahlung_vom v))
 >       gs = Gutschrift (gutschriftsbetrag v) (correct_date (gutschrift_vom v))
 
-> correct_date :: Datum -> Datum
-> correct_date d = d
 
 > eval_payment_sum :: Kassabucheintrag -> AP_Kassabucheintrag
-> eval_payment_sum k = k
+> eval_payment_sum (g, v) = (g, correct_sum v)
+
+> correct_date :: Datum -> Datum
+> correct_date d
+>   | monat d == Feb =
+>         if y `mod` 4 /= 0 && (day_to_int t) > 28 then fm
+>         else
+>            if y `mod` 100 == 0 && y `mod` 400 /= 0 then fm
+>            else
+>               if (day_to_int t) > 29 then fm
+>               else d
+>   | monat d == Dez && (day_to_int t) > 31 = ny
+>   | (day_to_int t) > 30 && not(monat d `elem` full_months) = nm
+>   | otherwise = d
+>   where
+>       y = jahr d
+>       t = tag d
+>       fm = D (int_to_day 1) Mar y
+>       nm = D (int_to_day 1) (int_to_month ((month_to_int (monat d)) + 1)) y
+>       ny = D (int_to_day 1) Jan (y + 1)
+
+> correct_sum :: Geschaeftsvorfall -> AP_Geschaeftsvorfall
+> correct_sum g = g
 
 Aufgabe A.2