howto: Change headline grammar

doc/HOWTO_IMPLEMENT_A_FUNCTOR.org

@@ -8,7 +8,7 @@ for concise technical documentation. Some basic Haskell knowledge is assumed.
 We're going to implement a simple version of the Powerset functor with functor
 syntax ~P(X)~ and morphism syntax ~{a, b, ...}~.
 
-* Create a Haskell module
+* Creating a Haskell module
 
 Create a new file called ~SimplePowerset.hs~ in the directory
 ~src/Copar/Functors/~ with the following content:
@@ -19,7 +19,7 @@ module Copar.Functors.SimplePowerset (simplePowerset) where
 
 and add the new module to the other functor modules in `copar.cabal`.
 
-* Create a datatype for the functor
+* Creating a datatype for the functor
 
 Let's create a new Haskell type for our functor:
 
@@ -68,7 +68,7 @@ stack exec -- copar help functors
 
 should now include the new =SimplePowerset= functor.
 
-* Implement the refinement Interface
+* Implementing the refinement Interface
 
 The refinement interface is the heart of our functor. It determines how
 partition refinement works for our type of transition system.
@@ -133,7 +133,7 @@ On the other hand, ~update~ is a little more complicated. It takes as arguments
 the list of labels of edges into a subblock, the ~Weight~ into the corresponding
 super block, and returns a tuple.
 
-* Implement a functor expression parser
+* Implementing a functor expression parser
 
 Each functor in CoPaR has a functor expression parser, which are combined to
 parse the first line of the input file to determine the functor for the
@@ -161,7 +161,7 @@ simplePowerset = FunctorDescription
   }
 #+END_SRC
 
-* Implement a morphism parser
+* Implementing a morphism parser
 
 The next thing the functor needs is a parser for the morphism syntax.