Hence, the answer is either 4, 5, 6 or 7. This is not too hard to show. A graph which can be represented so that vertices correspond to points in the plane and edges correspond to unit-length line ...

Let R be a ring. The unit graph of R, denoted by G (R), is the simple graph defined on all elements of R, and where two distinct vertices x and y are linked by an edge if and only if x+y is a unit of ...