Deductive way of reasoning about the internet AS level topology*
Szabó Dávida), Kőrösi Attilaa),c), Bíró Józsefa),b), Gulyás Andrása),c)
       
Illustration of valid (a) and invalid (b) valley-free path types. A valid path contains n customer–provider, at most 1 peer and m provider-customer link strictly in this order, where n , m ∈ ℕ. All the other types are invalid paths.