Section 4: Relations and cardinality constraints over entity types
change the first note description with the following equation:
if s1.user = s2.user -> s1.role != s2.role
In Referrential Integraty,
user-set
admin-user-set = { u E user-set | admin E roles(u)} admin-user-set != null
In relations,
role need to be changed to roles
if s1.user = s2.user -> s1.role != s2.role