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-rw-r--r--src/Cfe/Language/Properties.agda7
1 files changed, 7 insertions, 0 deletions
diff --git a/src/Cfe/Language/Properties.agda b/src/Cfe/Language/Properties.agda
index 61a11b2..6248e76 100644
--- a/src/Cfe/Language/Properties.agda
+++ b/src/Cfe/Language/Properties.agda
@@ -833,3 +833,10 @@ Fⁿ⊆⋃F = FⁿA⊆SupFA
⋃-inverseʳ : ∀ (A : Language a) → ⋃ (const A) ≈ A
⋃-inverseʳ _ = ⊆-antisym (sub λ {(ℕ.suc _ , w∈A) → w∈A}) (Fⁿ⊆⋃F 1)
+
+------------------------------------------------------------------------
+-- Other properties of Null
+------------------------------------------------------------------------
+
+∣w∣≡0+w∈A⇒ε∈A : ∀ {w} → length w ≡ 0 → w ∈ A → Null A
+∣w∣≡0+w∈A⇒ε∈A {w = []} _ ε∈A = ε∈A