diff --git a/music-parts.cabal b/music-parts.cabal
--- a/music-parts.cabal
+++ b/music-parts.cabal
@@ -1,6 +1,6 @@
 
 name:                   music-parts
-version:                1.6.2
+version:                1.7
 author:                 Hans Hoglund
 maintainer:             Hans Hoglund
 license:                BSD3
@@ -21,12 +21,14 @@
   location:             git://github.com/music-suite/music-parts.git
   
 library                    
-    build-depends:      base                    >= 4 && < 5,
+    build-depends:      base                    >= 4 &&   < 5,
+                        lens				            >= 4.1.2 && < 4.2,
+                        semigroups              >= 0.13.0.1 && < 1,
                         time,
                         random,
-                        semigroups              >= 0.13.0.1 && < 1,
                         semigroupoids,
                         data-default,
+                        adjunctions,
                         roman-numerals
     exposed-modules:    Music.Parts
                         -- Music.Parts.Strings
diff --git a/src/Music/Parts.hs b/src/Music/Parts.hs
--- a/src/Music/Parts.hs
+++ b/src/Music/Parts.hs
@@ -112,6 +112,10 @@
 import Data.Semigroup
 import Data.Typeable
 import Data.Maybe
+import Data.Traversable (traverse)
+import Control.Lens (toListOf)
+import Data.Functor.Adjunction (unzipR)
+import Control.Applicative
 import Text.Numeral.Roman (toRoman)
 import qualified Data.List
 
@@ -238,8 +242,14 @@
     toEnum x = Part Tutti (toEnum x) def
     fromEnum (Part solo instr subp) = fromEnum instr
 
+-- Semantics: Monoid (Option . First)
+instance Monoid Part where
+  mappend x _ = x
+  mempty = def
+instance Semigroup Part where
+  (<>) = mappend
 instance Default Part where
-    def = Part def def def
+  def = Part def def def
 
 -- | 
 -- @a \`containsPart\` b@ holds if the set of players represented by a is an improper subset of the 
@@ -400,14 +410,14 @@
     (30, (0,  5.0, 0,  "Distortion Guitar")),
     (31, (0,  5.0, 0,  "Guitar Harmonics")),
 
-    (32, (0,  8.0, 0,  "Acoustic Bass")),
-    (33, (0,  8.0, 0,  "Electric Bass (finger)")),
-    (34, (0,  8.0, 0,  "Electric Bass (pick)")),
-    (35, (0,  8.0, 0,  "Fretless Bass")),
-    (36, (0,  8.0, 0,  "Slap Bass 1")),
-    (37, (0,  8.0, 0,  "Slap Bass 2")),
-    (38, (0,  8.0, 0,  "Synth Bass 1")),
-    (39, (0,  8.0, 0,  "Synth Bass 2")),
+    (32, (0,  8.0, 2,  "Acoustic Bass")),
+    (33, (0,  8.0, 2,  "Electric Bass (finger)")),
+    (34, (0,  8.0, 2,  "Electric Bass (pick)")),
+    (35, (0,  8.0, 2,  "Fretless Bass")),
+    (36, (0,  8.0, 2,  "Slap Bass 1")),
+    (37, (0,  8.0, 2,  "Slap Bass 2")),
+    (38, (0,  8.0, 2,  "Synth Bass 1")),
+    (39, (0,  8.0, 2,  "Synth Bass 2")),
 
     (40, (12,  7.1, 0,  "Violin")),
     (41, (13,  7.2, 1,  "Viola")),
@@ -675,12 +685,44 @@
         | Pno
 
 -}
+-- TODO move
+instance Num a => Num (Option a) where
+  (+)       = liftA2 (+)
+  (-)       = liftA2 (-)
+  (*)       = liftA2 (*)
+  abs       = fmap abs
+  signum    = fmap signum
+  fromInteger = pure . fromInteger
+instance Integral a => Integral (Option a) where
+  quotRem x y = unzipR $ liftA2 quotRem x y
+  toInteger = toInteger . get where get = (head.toListOf traverse)
+instance Real a => Real (Option a) where
+  toRational = toRational . get where get = (head.toListOf traverse)
+instance Enum a => Enum (Option a) where
+  fromEnum = fromEnum . get where get = (head.toListOf traverse)
+  toEnum = pure . toEnum
 
+instance Num a => Num (First a) where
+  (+)       = liftA2 (+)
+  (-)       = liftA2 (-)
+  (*)       = liftA2 (*)
+  abs       = fmap abs
+  signum    = fmap signum
+  fromInteger = pure . fromInteger
+instance Integral a => Integral (First a) where
+  quotRem x y = unzipR $ liftA2 quotRem x y
+  toInteger = toInteger . get where get = (head.toListOf traverse)
+instance Real a => Real (First a) where
+  toRational = toRational . get where get = (head.toListOf traverse)
+-- instance Enum a => Enum (First a) where
+  -- toEnum = toEnum . get where get = (head.toListOf traverse)
+  -- fromEnum = pure . fromEnum
 
-newtype BasicPart = BasicPart { getBasicPart :: Integer }
-    deriving (Eq, Ord, Num, Integral, Real, Enum, Typeable)
+newtype BasicPart = BasicPart { getBasicPart :: Option (First Integer) }
+    deriving (Eq, Ord, Num, Integral, Real, Enum, Typeable, Semigroup, Monoid)
 
-instance Default BasicPart where def = BasicPart 0
+instance Default BasicPart where
+  def = mempty
 
 instance Show BasicPart where
     show _ = ""