Derive KnownNat constraints from other KnownNat constraints

 A type checker plugin for GHC that can derive "complex" KnownNat
 constraints from other simple/variable KnownNat constraints. i.e. without
 this plugin, you must have both a KnownNat n and a KnownNat (n+2)
 constraint in the type signature of the following function:
 .
 f :: forall n . (KnownNat n, KnownNat (n+2)) => Proxy n -> Integer
 f _ = natVal (Proxy :: Proxy n) + natVal (Proxy :: Proxy (n+2))
 .
 Using the plugin you can omit the KnownNat (n+2) constraint:
 .
 f :: forall n . KnownNat n => Proxy n -> Integer
 f _ = natVal (Proxy :: Proxy n) + natVal (Proxy :: Proxy (n+2))
 .
 The plugin can derive KnownNat constraints for types consisting of:
 .
  * Type variables, when there is a corresponding KnownNat constraint
 .
  * Type-level naturals
 .
  * Applications of the arithmetic expression: +,-,*,^
 .
  * Type functions, when there is either:
 .
 1. a matching given KnownNat constraint; or
 .
 2. a corresponding KnownNat<N> instance for the type function
 .
 To use the plugin, add the
 .
 OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver
 .
 Pragma to the header of your file.
 .
 This package provides a library for the Haskell programming language.
 See http://www.haskell.org/ for more information on Haskell.