Source: K. Riesen, Structural Pattern Recognition with Graph Edit Distance, Advances in Computer Vision and Pattern Recognition.
Below I want to ask clarification for an example in the text as it will help to understand when we say the edge is deleted and when we call it is substituted.
In the discussion of Example-8:
Deleting u1 costs 1, Substituting u2 by v3 will cost 2 (node substitution cost + deletion of (u1,u2)), Substituting u3 by v2 will cost 1 (node substitution, edge substitution: (u2,u3) by (v2,v3) ) and Substituting u4 by v1 will cost 2 (node substitution + deletion of (u2,u4)). So the total cost seems to be 6 but the text mentions it as 4.
I have also added the source as an image for convenience, thanks in advance!