ad aperturam libri
/ad ˌapəˈtʃʊərəm ˌlɪbri/adverb
With reference to an act of translation, a sermon, or other activity based on a text: extemporaneously, without preparation or recourse to reference materials.
Origin
Late 17th century. From post-classical Latin ad aperturam libri from classical Latin ad at + apertūram, accusative of apertūra + librī, genitive of liber book.