pred(data_structure,basic_programming).
pred(database,data_structure).
pred(adv_database,database).
pred(adv_database,logic).
pred(dataminig,adv_database).
pred(webminig,dataminig).
pred(design_algoritm,data_structure).
pred(ai,design_algoritm).
pred(datamining,ai).
prei(X,Y):-pred(X,Y).
prei(X,Y):-pred(X,Z),prei(Z,Y).