add-only-monotonic-dag.dl

.type id = symbol

// Example
.decl addBetween(U: id,V: id,W: id)
addBetween("|-","alpha","-|").
addBetween("|-","beta","delta").
addBetween("|-","delta","-|").
addBetween("delta","epsilon","-|").
addBetween("|-","gamma","delta").

// Query
.decl edge(U: id, V: id)
edge("|-","-|").
edge(U,V) :- edge(U,W), addBetween(U,V,W).
edge(V,W) :- edge(U,W), addBetween(U,V,W).

.decl path(U: id, V: id)
path(U,V) :- edge(U,V).
path(U,W) :- edge(U,V), path(V,W).

.decl vertex(V: id)
vertex(V) :- edge(V,_).
vertex(V) :- edge(_,V).

.output edge(IO=stdout)
.output vertex(IO=stdout)
.output path(IO=stdout)