diff --git a/presentation/presentation.md b/presentation/presentation.md
index 309cfed..ccf415f 100644
--- a/presentation/presentation.md
+++ b/presentation/presentation.md
@@ -141,4 +141,16 @@ end
 
 --- 
 
+## Interface
+
+```elixir
+receive do
+  {:start_game, paticipants} -> {:new_game, game, game_state}
+  {:make_move, game, participant, move} -> {:update_game, game, game_state} or {:game_finished, game}
+  {:get_game_state, game} -> {:game_state, game, game_state}
+end
+```
+
+---
+
 #### Questions?