Swi prolog finding all the neighbours of a nod in a directed graph -


i have directed graph represented this:

arc(1, 2). arc(1, 4). arc(1, 5). arc(3, 2). arc(3, 7). arc(4, 3). arc(5, 6). arc(6, 8). arc(7, 6). arc(9, 8).

what need predicate put inside list nodes can go specific node. example node 1 resulted list should l=[2,4,5] because 1 can go 2,4 , 5. doesn't matter how done, matters result, nodes must in list. have tried in couple of ways failed.

an example of how tried it: 

road(x,l,l2):- arc(x,y), not(belong(y,l)), append(l,[y],l2), road(x,l2,_).    road(x,l,l).

belong(y,l) predicate returns true if y found inside of l.
, example when run road(1,[],l). result l=[2], normal because predicate not written.
when try make using recursion don't know put right stop recursion, hope understand want say.
, tried way using fail didn't worked neither , don't remember how made it.
hope can come solution fast :), in advance.

your code need fair amount of corrections: here working version.

road(x,l,l2) :- arc(x,y), \+ memberchk(y,l), !, road(x,[y|l],l2). road(_,l,l).

it must called way , 'return' list reversed

?- road(1,[],l). l = [5, 4, 2] .

but it's easier - , efficient - use builtin:

?- findall(y, arc(1,y), l).

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