diff --git a/TODO.md b/TODO.md
index 0d057e4..f33dff8 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,7 +1,10 @@
 # net
 
+Transition -- has input and output places
 Place
-Transition
+Choice
+
+apply/applyTransition
 
 # lang
 
diff --git a/src/index.ts b/src/index.ts
deleted file mode 100644
index 09b76aa..0000000
--- a/src/index.ts
+++ /dev/null
@@ -1 +0,0 @@
-export const x = 1
diff --git a/src/lang/transition/Transition.ts b/src/lang/transition/Transition.ts
index dcc82e7..72ed1dd 100644
--- a/src/lang/transition/Transition.ts
+++ b/src/lang/transition/Transition.ts
@@ -1,3 +1,4 @@
 export type Transition = {
-  //
+  // input
+  // output
 }