Graph reachability

What this is? A self‑contained, browser‑only demo that answers the query ?- path(X, nantes) over a small directed graph of French cities using two Horn clauses:

C1: path(U,V) :- oneway(U,V).
C2: path(U,V) :- oneway(U,Z), path(Z,V).

Answer lists every city X that reaches nantes with one shortest chain. Reason shows a backward‑chaining proof for X = paris. Check validates the results by independent forward search and shortest‑path minimality.