diff --git a/TODO.md b/TODO.md
index 9e454af..577c46d 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,5 +1,3 @@
-findTransition & findTransitionEntryOrFail
-
 connectTransitionToInputs & connectTransitionToOutputs
 
 evaluateBlockStmt -- Connect
diff --git a/src/lang/net/findTransitionEntry.ts b/src/lang/net/findTransitionEntry.ts
new file mode 100644
index 0000000..7296ed5
--- /dev/null
+++ b/src/lang/net/findTransitionEntry.ts
@@ -0,0 +1,10 @@
+import { nodeKey } from "../node/nodeKey"
+import { Transition } from "../transition"
+import { Net, TransitionEntry } from "./Net"
+
+export function findTransitionEntry(
+  net: Net,
+  transition: Transition,
+): TransitionEntry | undefined {
+  return net.transitionEntries.get(nodeKey(transition))
+}
diff --git a/src/lang/net/findTransitionEntryOrFail.ts b/src/lang/net/findTransitionEntryOrFail.ts
new file mode 100644
index 0000000..835c347
--- /dev/null
+++ b/src/lang/net/findTransitionEntryOrFail.ts
@@ -0,0 +1,22 @@
+import { formatNode } from "../node"
+import { Transition } from "../transition"
+import { Net, TransitionEntry } from "./Net"
+import { findTransitionEntry } from "./findTransitionEntry"
+
+export function findTransitionEntryOrFail(
+  net: Net,
+  transition: Transition,
+): TransitionEntry {
+  const transitionEntry = findTransitionEntry(net, transition)
+  if (transitionEntry === undefined) {
+    throw new Error(
+      [
+        `[findTransitionEntryOrFail] I can not find nodeEntry for node.`,
+        ``,
+        `  transition: [${formatNode(net, transition)}]`,
+      ].join("\n"),
+    )
+  }
+
+  return transitionEntry
+}
diff --git a/src/lang/net/index.ts b/src/lang/net/index.ts
index 3d4b799..1fa8f0e 100644
--- a/src/lang/net/index.ts
+++ b/src/lang/net/index.ts
@@ -4,3 +4,5 @@ export * from "./addPlace"
 export * from "./addTransition"
 export * from "./findPlaceEntry"
 export * from "./findPlaceEntryOrFail"
+export * from "./findTransitionEntry"
+export * from "./findTransitionEntryOrFail"