I am ready Bondy and Murthy's Graph Theory:
And here is the Figure $1.10$:
I don't understand what are these three labelled graphs for $P_3$, in the figure, I see $4$ different graphs: $0$ edge, $1$ edge, $2$ edges, $3$ edges. Changing the labelling of the vertices would make three different graphs only if the number of edges is $1$ or $2$, isn't it?