diff --git a/Language/Graphs.agda b/Language/Graphs.agda
index 31f4afc..6504d6d 100644
--- a/Language/Graphs.agda
+++ b/Language/Graphs.agda
@@ -84,6 +84,18 @@ loop g = record g
               List.cartesianProduct (Graph.outputs g) (Graph.inputs g)
     }
 
+optional : Graph → Graph
+optional g = record
+    { size = 2 Nat.+ Graph.size g
+    ; nodes = [] ∷ [] ∷ Graph.nodes g
+    ; edges = (2 ↑ʳᵉ Graph.edges g) List.++
+              List.map (zero ,_) (2 ↑ʳⁱ Graph.inputs g) List.++
+              List.map (_, suc zero) (2 ↑ʳⁱ Graph.outputs g) List.++
+              ((zero , suc zero) ∷ [])
+    ; inputs = zero ∷ []
+    ; outputs = (suc zero) ∷ []
+    }
+
 infixr 5 _skipto_
 _skipto_ : Graph → Graph → Graph
 _skipto_ g₁ g₂ = record (g₁ ∙ g₂)
@@ -110,4 +122,4 @@ buildCfg : Stmt → Graph
 buildCfg ⟨ bs₁ ⟩ = singleton (bs₁ ∷ [])
 buildCfg (s₁ then s₂) = buildCfg s₁ ↦ buildCfg s₂
 buildCfg (if _ then s₁ else s₂) = singleton [] ↦ (buildCfg s₁ ∙ buildCfg s₂) ↦ singleton []
-buildCfg (while _ repeat s) = (loop (singleton [] ↦ buildCfg s)) skipto (singleton [])
+buildCfg (while _ repeat s) = optional (loop (buildCfg s))