anchor.diff:  
       open Starling.Core.Model.Pretty
       open Starling.Core.Command.Pretty
  +    open Starling.Core.Symbolic.Pretty
       open Starling.Core.View.Pretty
       open Starling.Core.GuardedView.Pretty
   
  
positive.code: ///     The new <c>Model</c>, over <c>GoalAxiom</c>s.
  /// </returns>
  let goalAdd
    (mdl : Model<Axiom<GView<Sym<Var>>, 'cmd>, _>)
    : Model<GoalAxiom<'cmd>, _> =
      // We use a fresh ID generator to ensure every goal variable is unique.
      let fg = freshGen ()
  
negative.code:                        ({ Axiom = a; Goal = f } : GoalAxiom<'cmd>)
                         : Doc =
          vsep [ headed "Axiom"
                        (a |> printAxiom (printIteratedGView (printSym String)) printCmd |> Seq.singleton)
                 headed "Goal" (f |> printOView |> Seq.singleton) ]
  
  
  