A graph can be expressed as an structure $G = <A,R>$ satisfying the axioms $ \forall xy R(x,y) \rightarrow R(y,x)$ and $ \forall x \lnot R(x,x)$.
How to extend the structure and/or axioms to express a 5 colourable graph?
A graph can be expressed as an structure $G = <A,R>$ satisfying the axioms $ \forall xy R(x,y) \rightarrow R(y,x)$ and $ \forall x \lnot R(x,x)$.
How to extend the structure and/or axioms to express a 5 colourable graph?
General ideas: