:d(X) :- :r(X,Y), def:0(Y)
def:0(X) :- all:0_1(X)
all:0_1(X) :- :s(X,Y), all:0_0(Y)
all:0_0(X) :- :s(X,Y), all:0_0(Y)
all:0_0(X) :- :c(X)