In chapter XXI, lines 115-116, of Lingua latina per se illustrata. Familia Romana (page 167) there is this sentence:
Nōn difficile est mātrem Mārcī fallere!
Its meaning is clear to me, but I'm not sure about its interpretation from the grammatical point of view.
I believe that difficile is the nominative singular neutral form of the adjective difficilis (that was for me something difficult to understand: at first, I thought it was an adverb). Then, I think (nōn) difficile est an impersonal construction similar to necesse est. There is an accusative: mātrem. So, I thought this was an example of the so called accusativus cum infinitivo structure. But I'm not at all sure about that. If I understand correctly, in the accusativus cum infinitivo construction, the accusative is the subject of the verb in the infinitive form. However, by context, in this case mātrem Mārcī is the direct object of fallere: it's Marcus who has cheated on his mother. Could someone help me clarify my doubt?