'Abtruse' is intended to signify 'complicated to understand' and 'perplexing'.
Yet math and philosophy use logic, which feels mathematical enough to fall under math.
A friend apprised me of a leading fee-paying UK high school's experiment for Sixth Formers (i.e. seniors) to substantiate 2.
Teachers notified all students that they'd be tested in 4 weeks, in 4.5 hours in class without notes, on 3 IMO questions from the Algebra section randomly selected from 2011-2016 papers whose solutions are posted.
They were advised to study the solutions, if they remained baffled after trying. Yet on the test, nobody solved 1 problem or finished early. When asked why, students said that IMO problems needed too clever tricks or inventions or "machinated ploys" (as one student complained).
After this IMO test, all students were instructed to read this list of unsolved philosophy problems for homework. In 2 weeks, they'd write a précis $\ge$ 300 words outlining the problems, on 4 randomly chosen topics from that list, in 2 hours in class without notes. Everyone aced this. Some finished before the time limit.
The snag: 4 weeks after this test, the teacher dispensed a pop test with the same format, but on another 4 randomly chosen topics. Yet everyone still aced it.