Solution: Early example of reductio ad absurdum - NYT Crossword

Ah, Saturday! When an abstruse clue must be translated before one can even ponder its equally arcane answer, which turns out to be something one’s never heard of, and it’s not even a debut in the puzzle. “Reductio ad absurdum” is a method of disproving a premise by showing that its logical consequence is impossible or self-contradictory. For example, I could say, “If Mark Diehl uses every letter of the alphabet in this grid, then I will eat my Panama hat!” As you already know, Mr. Diehl did use every letter in the alphabet in this grid, greatly aided by this entry, ZENOS PARADOX, which incorporates two of the most often omitted letters by constructors. And I do not even own a Panama hat to eat.