diff --git a/prototype/Doubt/Vertex.swift b/prototype/Doubt/Vertex.swift
index 094a08490..701c19f47 100644
--- a/prototype/Doubt/Vertex.swift
+++ b/prototype/Doubt/Vertex.swift
@@ -1,4 +1,4 @@
-public enum Vertex<Element> {
+public enum Vertex<Element>: CustomDebugStringConvertible {
 	indirect case XY(Element, Memo<Vertex>, Memo<Vertex>)
 	case End
 
@@ -88,4 +88,11 @@ public enum Vertex<Element> {
 			return .End
 		}
 	}
+
+
+	public var debugDescription: String {
+		return rowMajor.map {
+			$0.map { String(reflecting: $0) }.joinWithSeparator("\t")
+		}.joinWithSeparator("\n")
+	}
 }