diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,16 @@
 Changelog
 =========
 
+Version 0.2.6.1
+---------------
+
+*August 6, 2018*
+
+<https://github.com/mstksg/backprop/releases/tag/v0.2.6.1>
+
+*   Removed redundant constraints from `Floating` instance of `Op`.
+*   Fixed lower bound for *vinyl* dependency.
+
 Version 0.2.6.0
 ---------------
 
diff --git a/backprop.cabal b/backprop.cabal
--- a/backprop.cabal
+++ b/backprop.cabal
@@ -2,10 +2,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 5fe92f47f037a2d14b0df727ed7cb1213b58e39938cf6b691b376d5caa565d5d
+-- hash: 009a268e1d551f52673b7339f93986c16870d9402a854ad8157d133450ef7591
 
 name:           backprop
-version:        0.2.6.0
+version:        0.2.6.1
 synopsis:       Heterogeneous automatic differentation
 description:    Write your functions to compute your result, and the library will
                 automatically generate functions to compute your gradient.
@@ -63,7 +63,7 @@
     , reflection
     , transformers
     , vector
-    , vinyl >=0.9
+    , vinyl >=0.9.1
   exposed-modules:
       Numeric.Backprop
       Numeric.Backprop.Class
diff --git a/doc/01-getting-started.md b/doc/01-getting-started.md
--- a/doc/01-getting-started.md
+++ b/doc/01-getting-started.md
@@ -44,13 +44,13 @@
 They can be run with `evalBP`:
 
 ```haskell eval
-evalBP myFunc (9 :: Double)
+evalBP myFunc 9 :: Double
 ```
 
 And...the twist?  You can also get the gradient of your functions!
 
 ```haskell eval
-gradBP myFunc (9 :: Double)
+gradBP myFunc 9 :: Double
 ```
 
 We can even be cute with with the *[simple-reflect][]* library:
@@ -58,16 +58,20 @@
 [simple-reflect]: https://hackage.haskell.org/package/simple-reflect
 
 ```haskell top hide
+instance Backprop Expr where
+    zero = zeroNum
+    add  = addNum
+    one  = oneNum
 instance AskInliterate Expr
 ```
 
 ```haskell eval
-evalBP myFunc (x :: Expr)
+evalBP myFunc x :: Expr
 ```
 
 
 ```haskell eval
-gradBP myFunc (x :: Expr)
+gradBP myFunc x :: Expr
 ```
 
 
diff --git a/src/Numeric/Backprop/Op.hs b/src/Numeric/Backprop/Op.hs
--- a/src/Numeric/Backprop/Op.hs
+++ b/src/Numeric/Backprop/Op.hs
@@ -84,7 +84,6 @@
 import           Data.List
 import           Data.Type.Util
 import           Data.Vinyl.Core
-import           Data.Vinyl.TypeLevel
 import           Lens.Micro
 import           Lens.Micro.Extras
 import qualified Data.Vinyl.Recursive  as VR
@@ -330,7 +329,10 @@
 --
 -- @since 0.1.3.0
 noGrad1 :: (a -> b) -> Op '[a] b
-noGrad1 f = op1 (\x -> (f x, \_ -> error "noGrad1: no gradient defined"))
+noGrad1 f = op1 $ \x ->
+    ( f x
+    , \_ -> errorWithoutStackTrace "Numeric.Backprop.Op.noGrad1: no gradient defined"
+    )
 {-# INLINE noGrad1 #-}
 
 -- | Create an 'Op' with no gradient.  Can be evaluated with 'evalOp',  but
@@ -347,7 +349,10 @@
 --
 -- @since 0.1.3.0
 noGrad :: (Rec Identity as -> b) -> Op as b
-noGrad f = Op (\xs -> (f xs, \_ -> error "noGrad: no gradient defined"))
+noGrad f = Op $ \xs ->
+    ( f xs
+    , \_ -> errorWithoutStackTrace "Numeric.Backprop.Op.noGrad: no gradient defined"
+    )
 {-# INLINE noGrad #-}
 
 -- | An 'Op' that just returns whatever it receives.  The identity
@@ -423,7 +428,7 @@
     => a
     -> Op as a
 opConst x = Op $ const
-    (x , const $ rpureConstrained @Num 0)
+    (x, const $ rpureConstrained @Num 0)
 {-# INLINE opConst #-}
 
 -- | Create an 'Op' that takes no inputs and always returns the given
@@ -566,7 +571,7 @@
     fromRational x = opConst (fromRational x)
     {-# INLINE fromRational #-}
 
-instance (RecApplicative as, AllConstrained Floating as, AllConstrained Fractional as, AllConstrained Num as, RPureConstrained Num as, Floating a) => Floating (Op as a) where
+instance (RPureConstrained Num as, Floating a) => Floating (Op as a) where
     pi            = opConst pi
     {-# INLINE pi #-}
     exp   o       = composeOp (o  :& RNil)       expOp