 Hammer and Shin take a different path from these revisions: To revive Euler’s homomorphic relation between circles and sets—containment among circles represents the subset relation among sets, and non-overlapping of regions represents the disjoint relation—and at the same time, to adopt Venn’s primary diagrams by default. On the other hand, this revised Euler system is not a self-sufficient tool for syllogistic reasoning, since it cannot represent existential statements. For more details of this revised system, refer to (Hammer &amp; Shin  1998).