dependsOn(church,newton).
dependsOn(church,euler).
dependsOn(weyl,newton).
dependsOn(newton,scienceRouter).
dependsOn(scienceRouter,grinnellRouter).
dependsOn(euler,scienceRouter).
dependsOn(grinnellRouter,hunkOcable).
dependsOn(hunkOcable,iowaState).

pcof(X,Y) :- dependsOn(X,Y).
pcof(X,Y) :- dependsOn(X,Z), pcof(Z,Y).