οὐδὲ θέμις εἴη αἰτεῖσθαι παρὰ τῶν θεῶν οὔτε ἱππεύειν μὴ μαθόντας ἱππομαχοῦντας νικᾶν, etc.
Acording to the lexicons, you would expect D and inf with θέμις, and not Acc cum inf. I thought that there might be a difference in meaning like it is not right for those who have not learned horsemanship to pray to the gods asking to give them a victory in a cavalry battle (with D) vs it is not right that those who have not learned horsemanship pray to the gods asking to give them a victory in a cavalry battle (with Acc), but the English translation makes no distinction.
I guess if you wanted to make a distinction you could translate the accusative version: it’s not right to ask the gods that those who don’t know how to ride a horse win a cavalry battle.
yes this is what i meant.