---
tag: 5YARHEWPAR
kind: concept
name: Second order
sources:
  - wikipedia: en:325802@r1373839425
    locator: Glossary of graph theory, section S
    note: adopted
    mention: wikipedia://en/325802#AL8X
    sections: [Summary]
inventory: [WC4QA76NE4]
---

## Summary

The second order logic of graphs is a form of logic in which variables may represent vertices, edges, sets of vertices, and (sometimes) sets of edges. This logic includes predicates for testing whether a vertex and edge are incident, as well as whether a vertex or edge belongs to a set. To be distinguished from first order logic, in which variables can only represent vertices.