Pseudographs
A pseudograph is a triple (V,E,f) (sometimes written just as (V,E))
- V is a nonemty set, whose elements are called vertices (singular -
- E is a (possibly empty) set, whose elements are called edges;
- f is a function from E to {{u,v} | u,v?V}.
By abuse of terminology, we sometimes identify e with f(e).
An edge e is said to be a loop if f(e)={u,u}={u} for some u?V.
The edges e1 and e2 are called multiple or parallel if f(e1)=f(e2).
v2 here, e3 and e4 are parallel;