Assume that X(G) is a graph obtained from the graph G using some definition. Unlike the line graph L(G) of a graph G.

Which one is sensible to write grammatically? 

Theorem: The graph X(G) of a graph G is planar if and only if G is the path P3 and P4. 

OR

Theorem: The graph X(G) of a graph G is planar if and only if G is a path P3 and P4.