1 files changed, 2 insertions, 0 deletions

diff --git a/bank-eiffel/studentaccount.e b/bank-eiffel/studentaccount.e
index 831cb6a..a80d4bb 100644
--- a/bank-eiffel/studentaccount.e
+++ b/bank-eiffel/studentaccount.e
@@ -10,4 +10,6 @@ class
 inherit
         ACCOUNT
 
+invariant
+        authorized_signers_only_one: authorized_signers.count = 1
 end