【演習問題７：群論``単位元'' (TPTP/GRP003-1)】

dom(A)-->product(inverse(A),A,identity).
dom(A)-->product(identity,A,A).

product(A,B,C),product(B,D,E),product(C,D,F)-->product(A,E,F).
product(A,B,C),product(B,D,E),product(A,E,F)-->product(C,D,F).

product(a,identity,a)-->false.

true-->dom(identity),dom(a).
dom(A)-->dom(inverse(A)).