Covering and overlapping constraints
The generalization


follows the covering constraint, so: E1 ⋃ E2 ⋃ E3 = E0
does not follow the overlapping 'constraint' ⇒ is disjoint,  so: E1 ⋂ E2 ⋂ E3 = ∅ 


The maximum and minimum amount of entities in E0 is 60. Since no overlapping is allowed there will be 15 + 20 + 25 = 60 distinct entities, which are all entities of superentity E0 at the same time because of the covering constraint.



E1 ⋃ E2 ⋃ E3 = E0 ⇒  max{|E1|, |E2|, |E3|}  &le; |E0| &le; |E1| + |E2| + |E3|

(E1 ⋃ E2 ⋃ E3 = E0  ⋀ E1 ⋂ E2 ⋂ E3 = ∅) ⇒ |E0| = |E1 + E2 + E3|