Slaughtering Competition Problems with Quantifier Elimination

Sage turns scary math into push-button answers and purists are fuming

TLDR: A mathematician shows how Sage + QEPCAD can turn tricky contest inequalities into quick, computer-checked facts. Commenters battled over whether this is genius modern math or joyless cheat codes, with memes, install woes, and a split between proof purists and tool-loving pragmatists.

Chris Grossack just dropped a math mic: use Sage + QEPCAD (a tool that removes the tricky “for all/there exists” parts of a statement) to smash those contrived competition inequalities. The post shows how a computer can check hard-looking claims—like the MSE inequality—then instantly confirm the equality cases with a couple of lines. Cue chaos. The comment crowd split fast. Purists called it academic cheat codes, saying contests are about crafting clever proofs, not pressing a “nuke” button. Pragmatists fired back: computers are part of modern math—why gatekeep tools that teach and verify? One meme had Tarski (the theorems behind this trick) as a giant kaiju stomping Olympiad problems, with “sage -i qepcad” as the red launch switch. Others joked it’s “Math Olympiad speedrun%” and “press X to eliminate quantifiers.” There was even install drama: half the thread flexed their smooth setup; the other half claimed QEPCAD is an ancient beast that only installs if the planets align. Fans loved the clarity—quantifier elimination turns foggy algebra into simple checks. Critics warned it can kill intuition. Either way, the mood was loud, geeky, and hilarious, and the computer absolutely did the homework.

Key Points

  • The post explains quantifier elimination and cites the Tarski–Seidenberg theorem as its foundation.
  • SageMath’s interface to QEPCAD is used to automatically eliminate quantifiers from polynomial formulas.
  • An example shows ∃x: ax^2 + bx + c = 0 is equivalent to b^2 − 4ac ≥ 0.
  • A competition-style inequality with a^4 + b^4 = 17 is verified by rewriting to polynomials and applying QEPCAD.
  • Equality cases for the inequality are checked, confirming only (1,2) and (2,1) achieve equality.

Hottest takes

“If your proof starts with ‘sage -i qepcad,’ you’re speedrunning math” — ProofPurist
“Tools aren’t cheating—refusing them is. Welcome to 2021” — ComputeGoblin
“Tarski is OP. Olympiad graders are crying in a corner” — TerminalEnjoyer
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