Index: sql/schema.md
===================================================================
--- sql/schema.md	(revision 1a9c843acf41686a27bf5c58dc77ace2cf638132)
+++ sql/schema.md	(revision bcacc91b5770933c5f080d279be105c850b2ece9)
@@ -111,4 +111,5 @@
     payment {
         integer id PK
+        integer user_id FK
         integer enrollment_id FK
         integer amount
@@ -135,4 +136,5 @@
     users               ||--o| contact            : has_contact
     users               ||--o{ token              : has_token
+    users               ||--o{ payment            : pays
     users               ||--o{ enrolled_semesters : submits
     users               ||--o{ user_documents     : owns
@@ -182,5 +184,2 @@
   they differ.
 - `professour_subjects` keeps the spelling used by the table in `schema_creation.sql`.
-- `payment` has no `user_id`: the student is reached through `enrollment_id`.
-  Storing it twice violated BCNF (`enrolled_id -> user_id`) and allowed a
-  payment to contradict the enrolment it refers to. Removed in Phase 5.