тайна за семью печатями(a subject or problem that someone does not know about or understand. Например: Mathematics has always been a closed book to me. teterevaann)
без использования справочного материала(adj. referring to exams in which external resources such as glossaries, study notes, calculators, etc are prohibited At the final level folks had to write a closed-book exam. The researchers seemed impressed that practice retrieving facts worked better than making concept maps with the text in front of them at preparing students for a closed-book test even when the test itself involved making concept maps. I am sorry to inform you that there will be a closed-book final examination at the end of the course. wordnik.comAlexander Demidov)
