% principal ID (Acme)
isPrincipal(acme).
% principal ID (Coyote)
isPrincipal(coyote).

%Acme.buy_rockets <- Acme.preferred_customer
isMember(Z, role(acme, buy_rockets, ["cert2", C] )) :- 
           isMember(Z, role(acme, preferred_customer, [C])). 

%Acme.preferred_customer <- Coyote
isMember(coyote, role(acme, preferred_customer, ["cert1"])).

%--role preferred_customer --principal coyote
%isMember(coyote, role(acme, preferred_customer, C)).
%isMember(coyote, role(acme, buy_rockets, C)).