The Analyst by Bishop George Berkeley, the famous pamphlet against vagueness of early Analysis, ends with a list of 67 Queries. Quite a number of them, in my humble opinion, remain unanswered, this one in particular:
Qu. 38. Whether tedious Calculations in Algebra and Fluxions be the likeliest Method to improve the Mind? And whether Mens being accustomed to reason altogether about Mathematical Signs and Figures, doth not make them at a loss how to reason without them?