#hide.
#external hc(X,Y).
#show hc(X,Y).     %% input
#show reached(X).  %% output (can alternatively remain hidden)
#domain node(X;Y).
#options -d none.

node(1..n). {hc(X,Y)}.  %% for grounding

initialnode(1).
reached(Y) :- hc(X,Y), reached(X), not initialnode(X). 
reached(Y) :- hc(X,Y), initialnode(X).
:- not reached(X).