unweighted-graph/adj missing vertices

[stchang]

Thanks @skbach.

1.) Adjacency lists are failing as graphs for many other functions.

(define adj (unweighted-graph/adj '((a b c) (b c d))))
(dag? adj) ; => crash

(bellman-ford adj 'a) ; => crash

2.) Destination vertices of an adjacency list aren't reported as vertices.

(define g (unweighted-graph/adj '((a b) (a c) (b c))))
(in-vertices g)
'(a b) ;; should have 'c

(sequence->list (in-edges g))
'((a c) (b c)) ;; should have '(a b)

[stchang]

Note, in the second item above, 'a has two adjacency lists but I think this is fine. The neighbors will be unioned together.