satz  --> subjekt, verb, objekt.

subjekt --> artikel, substantiv.

objekt  --> artikel, substantiv.

artikel --> [die].
artikel --> [eine].

substantiv --> [katze].
substantiv --> [maus].

verb  --> [jagt].
verb  --> [beisst].


abcs --> as, bs, cs.

as --> [a].
as --> [a], as.

bs --> [b].
bs --> [b], bs.

cs --> [c].
cs --> [c], cs.

abcequal --> as(A), bs(B), cs(C), { A=:=B, B=:=C }.

as(1)   --> [a].
as(N+1) --> [a], as(N).

bs(1)   --> [b].
bs(N+1) --> [b], bs(N).

cs(1)   --> [c].
cs(N+1) --> [c], cs(N).
