diff --git a/dhall/Decimal.dhall b/dhall/Decimal.dhall
new file mode 100644
index 0000000..5d184c6
--- /dev/null
+++ b/dhall/Decimal.dhall
@@ -0,0 +1,147 @@
+let Nat =
+      https://prelude.dhall-lang.org/v21.1.0/Natural/package.dhall
+        sha256:ee9ed2b28a417ed4e9a0c284801b928bf91b3fbdc1a68616347678c1821f1ddf
+
+let Int =
+      https://prelude.dhall-lang.org/v21.1.0/Integer/package.dhall
+        sha256:d1a572ca3a764781496847e4921d7d9a881c18ffcfac6ae28d0e5299066938a0
+
+let T = ./Types.dhall
+
+let M = ./math.dhall
+
+let dec =
+      \(s : Bool) ->
+      \(w : Natural) ->
+      \(d : Natural) ->
+      \(p : Natural) ->
+        { whole = w, decimal = d, precision = p, sign = s } : T.Decimal
+
+let dec2 = \(s : Bool) -> \(w : Natural) -> \(d : Natural) -> dec s w d 2
+
+let d = dec2 True
+
+let d_ = dec2 False
+
+let Decimal/toNatural =
+      \(a : T.Decimal) ->
+        let p = M.Natural/pow 10 a.precision in a.whole * p + a.decimal
+
+let Decimal/toInteger =
+      \(x : T.Decimal) ->
+        let n = Nat.toInteger (Decimal/toNatural x)
+
+        in  if x.sign == True then n else Int.negate n
+
+let Decimal/add
+    : T.Decimal -> T.Decimal -> T.Decimal
+    = \(a : T.Decimal) ->
+      \(b : T.Decimal) ->
+        let final_precision = Nat.max a.precision b.precision
+
+        let to_int =
+              \(z : T.Decimal) ->
+                Decimal/toInteger
+                  (     z
+                    //  { precision = final_precision
+                        , decimal =
+                              z.decimal
+                            * M.Natural/pow
+                                10
+                                (Nat.subtract z.precision final_precision)
+                        }
+                  )
+
+        let x = to_int a
+
+        let y = to_int b
+
+        let p = M.Natural/pow 10 final_precision
+
+        let res = M.Integer/quotRemUnsafe p (Int.add x y)
+
+        in  dec
+              (Int.positive res.quotiant)
+              (Int.abs res.quotiant)
+              (Int.abs res.remainder)
+              final_precision
+
+let test =
+      assert : Decimal/add (dec True 1 0 0) (dec True 1 0 0) === dec True 2 0 0
+
+let test =
+        assert
+      : Decimal/add (dec True 1 5 1) (dec False 2 0 0) === dec False 0 5 1
+
+let Decimal/multiply
+    : T.Decimal -> T.Decimal -> T.Decimal
+    = \(a : T.Decimal) ->
+      \(b : T.Decimal) ->
+        let x = Decimal/toNatural a
+
+        let y = Decimal/toNatural b
+
+        let p = a.precision + b.precision
+
+        let res = M.Natural/quotRemUnsafe (M.Natural/pow 10 p) (x * y)
+
+        in  dec (a.sign == b.sign) res.quotiant res.remainder p
+
+let test =
+        assert
+      : Decimal/multiply (dec True 1 0 1) (dec True 0 0 0) === dec True 0 0 1
+
+let test =
+        assert
+      : Decimal/multiply (dec True 1 0 1) (dec True 1 0 0) === dec True 1 0 1
+
+let test =
+        assert
+      :     Decimal/multiply (dec True 1 4 1) (dec False 2 0 2)
+        ===  dec False 2 800 3
+
+let Decimal/round
+    : Natural -> T.Decimal -> T.Decimal
+    = \(p : Natural) ->
+      \(a : T.Decimal) ->
+        if    Nat.equal a.precision p
+        then  a
+        else  if Nat.greaterThan p a.precision
+        then      a
+              //  { precision = p
+                  , decimal =
+                      a.decimal * M.Natural/pow 10 (Nat.subtract a.precision p)
+                  }
+        else  let subp = M.Natural/pow 10 (Nat.subtract (p + 1) a.precision)
+
+              let subRes =
+                    M.Natural/quotRem
+                      10
+                      M.QED
+                      (M.Natural/quotRemUnsafe subp a.decimal).quotiant
+
+              in  if    Nat.lessThan subRes.remainder 5
+                  then  a // { precision = p, decimal = subRes.quotiant }
+                  else  let dec = subRes.quotiant + 1
+
+                        in  if    Nat.equal dec (M.Natural/pow 10 p)
+                            then      a
+                                  //  { whole = a.whole + 1
+                                      , decimal = 0
+                                      , precision = p
+                                      }
+                            else  a // { decimal = dec, precision = p }
+
+let test = assert : Decimal/round 2 (dec True 0 49 2) === dec True 0 49 2
+
+let test = assert : Decimal/round 1 (dec True 0 49 2) === dec True 0 5 1
+
+let test = assert : Decimal/round 0 (dec True 0 49 2) === dec True 0 0 0
+
+let test =
+        assert
+      : Decimal/round 3 (dec True 0 49 2) === Decimal/round 3 (dec True 0 490 3)
+
+let test = assert : Decimal/round 1 (dec True 0 95 2) === dec True 1 0 1
+
+in  { dec, dec2, d, d_, Decimal/add, Decimal/multiply, Decimal/round }
diff --git a/dhall/common.dhall b/dhall/common.dhall
index 0870988..99aa669 100644
--- a/dhall/common.dhall
+++ b/dhall/common.dhall
@@ -4,6 +4,10 @@ let List/map =
 
 let T = ./Types.dhall
 
+let D = ./Decimal.dhall
+
+let M = ./math.dhall
+
 let nullSplit =
       \(a : T.SplitAcnt) ->
       \(c : T.SplitCur) ->
@@ -112,19 +116,6 @@ let part1_ =
       \(a : T.SplitAcnt) ->
         partN c a "" ([] : List PartSplit)
 
-let dec =
-      \(s : Bool) ->
-      \(w : Natural) ->
-      \(d : Natural) ->
-      \(p : Natural) ->
-        { whole = w, decimal = d, precision = p, sign = s } : T.Decimal
-
-let dec2 = \(s : Bool) -> \(w : Natural) -> \(d : Natural) -> dec s w d 2
-
-let d = dec2 True
-
-let d_ = dec2 False
-
 let addDay =
       \(x : T.GregorianM) ->
       \(d : Natural) ->
@@ -170,8 +161,6 @@ in      { nullSplit
         , partN
         , part1
         , part1_
-        , d
-        , d_
         , addDay
         , comma = 44
         , tab = 9
@@ -186,3 +175,5 @@ in      { nullSplit
         , PartSplit
         }
     /\  T
+    /\  D
+    /\  M
diff --git a/dhall/math.dhall b/dhall/math.dhall
new file mode 100644
index 0000000..53cf7e6
--- /dev/null
+++ b/dhall/math.dhall
@@ -0,0 +1,192 @@
+let Nat =
+      https://prelude.dhall-lang.org/v21.1.0/Natural/package.dhall
+        sha256:ee9ed2b28a417ed4e9a0c284801b928bf91b3fbdc1a68616347678c1821f1ddf
+
+let Int =
+      https://prelude.dhall-lang.org/v21.1.0/Integer/package.dhall
+        sha256:d1a572ca3a764781496847e4921d7d9a881c18ffcfac6ae28d0e5299066938a0
+
+let foldWhile
+    : forall (n : Natural) ->
+      forall (res : Type) ->
+      forall (succ : res -> Optional res) ->
+      forall (zero : res) ->
+        res
+    = \(n : Natural) ->
+      \(R : Type) ->
+      \(succ : R -> Optional R) ->
+      \(zero : R) ->
+        let Acc
+            : Type
+            = { current : R, done : Bool }
+
+        let update
+            : Acc -> Acc
+            = \(acc : Acc) ->
+                if    acc.done
+                then  acc
+                else  merge
+                        { Some = \(r : R) -> acc // { current = r }
+                        , None = acc // { done = True }
+                        }
+                        (succ acc.current)
+
+        let init
+            : Acc
+            = { current = zero, done = False }
+
+        let result
+            : Acc
+            = Natural/fold n Acc update init
+
+        in  result.current
+
+let DivRes = \(a : Type) -> { remainder : a, quotiant : a }
+
+let QED = assert : True === True
+
+let downwardSteps =
+      \(x : Natural) ->
+      \(y : Natural) ->
+        let initAcc
+            : DivRes Natural
+            = { remainder = x, quotiant = 0 }
+
+        let updateAcc
+            : DivRes Natural -> Optional (DivRes Natural)
+            = \(acc : DivRes Natural) ->
+                if    Nat.lessThan acc.remainder y
+                then  None (DivRes Natural)
+                else  Some
+                        { remainder = Natural/subtract y acc.remainder
+                        , quotiant = acc.quotiant + 1
+                        }
+
+        in  foldWhile (x + 1) (DivRes Natural) updateAcc initAcc
+
+let Natural/quotRemUnsafe
+    : forall (a : Natural) -> Natural -> DivRes Natural
+    = \(x : Natural) -> \(y : Natural) -> downwardSteps y x
+
+let Natural/quotRem
+    : forall (a : Natural) ->
+      Nat.isZero a == False === True ->
+      Natural ->
+        DivRes Natural
+    = \(x : Natural) ->
+      \(_ : Nat.isZero x == False === True) ->
+      \(y : Natural) ->
+        Natural/quotRemUnsafe x y
+
+let Natural/div
+    : forall (a : Natural) ->
+      Nat.isZero a == False === True ->
+      Natural ->
+        Natural
+    = \(x : Natural) ->
+      \(a : Nat.isZero x == False === True) ->
+      \(y : Natural) ->
+        (Natural/quotRem x a y).quotiant
+
+let d1 = assert : Natural/div 1 QED 1 === 1
+
+let d2 = assert : Natural/div 2 QED 1 === 0
+
+let d3 = assert : Natural/div 2 QED 5 === 2
+
+let Natural/rem
+    : forall (a : Natural) ->
+      Nat.isZero a == False === True ->
+      Natural ->
+        Natural
+    = \(x : Natural) ->
+      \(a : Nat.isZero x == False === True) ->
+      \(y : Natural) ->
+        (Natural/quotRem x a y).remainder
+
+let r1 = assert : Natural/rem 2 QED 4 === 0
+
+let r2 = assert : Natural/rem 2 QED 5 === 1
+
+let Natural/pow
+    : Natural -> Natural -> Natural
+    = \(b : Natural) ->
+      \(p : Natural) ->
+        Natural/fold p Natural (\(x : Natural) -> x * b) 1
+
+let p1 = assert : Natural/pow 10 1 === 10
+
+let p2 = assert : Natural/pow 10 3 === 1000
+
+let p3 = assert : Natural/pow 10 0 === 1
+
+let Integer/quotRemUnsafe
+    : Natural -> Integer -> DivRes Integer
+    = \(x : Natural) ->
+      \(y : Integer) ->
+        if    Int.equal y +0
+        then  { quotiant = +0, remainder = +0 }
+        else  let sign = if Int.positive y then +1 else -1
+
+              let toInt = \(x : Natural) -> Int.multiply sign (Nat.toInteger x)
+
+              let res = Natural/quotRemUnsafe x (Int.abs y)
+
+              in  { quotiant = toInt res.quotiant
+                  , remainder = toInt res.remainder
+                  }
+
+let Integer/quotRem
+    : forall (a : Natural) ->
+      Nat.isZero a == False === True ->
+      Integer ->
+        DivRes Integer
+    = \(x : Natural) ->
+      \(_ : Nat.isZero x == False === True) ->
+      \(y : Integer) ->
+        Integer/quotRemUnsafe x y
+
+let Integer/div
+    : forall (a : Natural) ->
+      Nat.isZero a == False === True ->
+      Integer ->
+        Integer
+    = \(x : Natural) ->
+      \(a : Nat.isZero x == False === True) ->
+      \(y : Integer) ->
+        (Integer/quotRem x a y).quotiant
+
+let id1 = assert : Integer/div 1 QED +3 === +3
+
+let id2 = assert : Integer/div 1 QED -3 === -3
+
+let id3 = assert : Integer/div 2 QED -7 === -3
+
+let Integer/rem
+    : forall (a : Natural) ->
+      Nat.isZero a == False === True ->
+      Integer ->
+        Integer
+    = \(x : Natural) ->
+      \(a : Nat.isZero x == False === True) ->
+      \(y : Integer) ->
+        (Integer/quotRem x a y).remainder
+
+let ir1 = assert : Integer/rem 1 QED +3 === +0
+
+let ir2 = assert : Integer/rem 1 QED -3 === -0
+
+let ir3 = assert : Integer/rem 2 QED -7 === -1
+
+in  { QED
+    , DivRes
+    , Natural/div
+    , Natural/rem
+    , Natural/quotRem
+    , Natural/quotRemUnsafe
+    , Natural/pow
+    , Integer/quotRem
+    , Integer/quotRemUnsafe
+    , Integer/div
+    , Integer/rem
+    }