: Another historical reference is Dificuldades da Língua Portuguesa , published by the Brazilian Academy of Letters, which explores the historical evolution and literary usage of problematic terms. Related Academic Research
: Research papers such as "Is Portuguese Really Difficult?" analyze specific complexities like pronoun placement and the inflected infinitive, which are core topics in "difficulty" dictionaries. DicionГЎrio de Dificuldades da LГngua Portuguesa
If you are looking for research papers analyzing the complexity or teaching of these difficulties, consider these themes found in scholarly databases like SciELO or ResearchGate : : Another historical reference is Dificuldades da Língua