9.5 Graph Filters
procedure
(graph-distinct-statements graph) → (set/c statement?)
graph : graph? 
TBD
procedure
(graph-distinct-subjects graph) → (set/c subject?)
graph : graph? 
TBD
procedure
(graph-distinct-predicates graph) → (set/c predicate?)
graph : graph? 
TBD
procedure
(graph-distinct-objects graph) → (set/c object?)
graph : graph? 
TBD
procedure
(graph-filter graph proc) → statement-list?
graph : graph? proc : (-> statement? boolean?) 
TBD
procedure
(graph-filter-by-subject graph val) → statement-list?
graph : graph? val : subject? 
TBD
procedure
(graph-filter-by-predicate graph val) → statement-list?
graph : graph? val : predicate? 
TBD
procedure
(graph-filter-by-object graph val) → statement-list?
graph : graph? val : object? 
TBD