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I recently played a bullet game, in which I thought I was in checkmate, but then realized I had one legal move, this then repeated again and again 6 times until ultimately I was in checkmate. I share this anecdote as an explanation for the seemingly arbitrary parameters.

To reiterate, one player (black or white) puts the other player in check. That player has only one legal move (moving the king, blocking the check, or capturing the attacking piece) Then the other player puts them in the same circumstance of one legal move. Player one does not need to be put in check or have their moves limited, only in the sense that no positions may be repeated.

The final check of the sequence is checkmate.

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  • 1
    To be clear, are repeated positions allowed or do you want the checking player to have to make a move that results in a different position each time? Depending on your answer, I can be real crafty with the 50 move rule and threefold repetition.
    – Rewan Demontay
    Mar 5 at 21:17
  • 1
    Hello Rewan, to clarify, no repeated positions are allowed. The purpose of this challenge is to create a long series of unique positions that "look like mate" (though this subjective quality is not an actual requirement) before the final checkmate.
    – Mur
    Mar 7 at 0:46
  • The requirement of 'unique moves' is a bit mysterious, especially as there already is a requirement of non-repeating positions, which seems to cover the same ground. Are they two separate requirements? Or... ?
    – user30536
    Mar 7 at 11:17
  • @user30536 Two ways of expressing the same idea, that's all.
    – Rewan Demontay
    Mar 7 at 21:25
  • @user30536 yes just one requirement, i'm not really a math guy hence the mystery :)
    – Mur
    Apr 6 at 18:09

1 Answer 1

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7

Here is such a sequence of 627 moves. With some trickery utilizing captures, each position is indeed unique. Many thanks goes to @Noam D. Elkies for suggesting improvements.

[Title "me, chess.stack.exchange.com, 3/7/2023"]
[FEN "8/8/8/pp1NN3/1p1KN3/1p6/nnppp1R1/1b3Qbk w - - 0 1"]

1. Rxg1+ Kh2 2. Qf2+ Kh3 3. Rg3+ Kh4 4. Qf4+ Kh5 5. Rg5+ Kh6 6. Qf6+ Kh7 7. Rg7+ Kh8 8. Rf7+ Kg8 9. Qg5+ Kh8 10. Qh4+ Kg8 11. Qg3+ Kh8 12. Qh2+ Kg8 13. Qg1+ Kh8 14. Qh1+ Kg8 15. Qg2+ Kh8 16. Qh3+ Kg8 17. Qg4+ Kh8 18. Qh5+ Kg8 19. Qg6+ Kh8 20. Qh6+ Kg8 21. Rg7+ Kf8 22. Qf6+ Ke8 23. Re7+ Kd8 24.Qd6+ Kc8 25. Rc7+ Kb8 26. Qb6+ Ka8 27. Qxa5+ Kb8 28. Qb6+ Ka8 29. Qa6+ Kb8 30. Rb7+ Kc8 31. Qc6+ Kd8 32. Rd7+ Ke8 33. Qe6+ Kf8 34. Rf7+ Kg8 35. Qg6+ Kh8 36. Qh5+ Kg8 37. Qg4+ Kh8 38. Qh3+ Kg8 39. Qg2+ Kh8 40. Qh1+ Kg8 41. Qg1+ Kh8 42. Qh2+ Kg8 43. Qg3+ Kh8 44. Qh4+ Kg8 45. Qg5+ Kh8 46. Qf6+ Kg8 47. Rg7+ Kh8 48. Rg6+ Kh7 49. Qf7+ Kh8 50. Qe8+ Kh7 51. Qd7+ Kh8 52. Qc8+ Kh7 53. Qb7+ Kh8 54. Qa8+ Kh7 55. Qa7+ Kh8 56. Qb8+ Kh7 57. Qc7+ Kh8 58. Qd8+ Kh7 59. Qe7+ Kh8 60. Qf8+ Kh7 61. Rg7+ Kh6 62. Qf6+ Kh5 63. Rg5+ Kh4 64. Qf4+ Kh3 65. Rg3+ Kh2 66. Qf2+ Kh1 67. Qf3+ Kh2 68. Rg2+ Kh1 69. Rxe2+ Kg1 70. Rg2+ Kh1 71. Rg3+ Kh2 72. Qf2+ Kh1 73. Qf1+ Kh2 74. Rg2+ Kh3 75. Qf3+ Kh4 76. Rg4+ Kh5 77. Qf5+ Kh6 78. Rg6+ Kh7 79. Qf7+ Kh8 80. Qe8+ Kh7 81. Qd7+ Kh8 82. Qc8+ Kh7 83. Qb7+ Kh8 84. Qa8+ Kh7 85. Qa7+ Kh8 86. Qb8+ Kh7 87. Qc7+ Kh8 88. Qd8+ Kh7 89. Qe7+ Kh8 90. Qf6+ Kh7 91. Rg7+ Kh8 92. Rf7+ Kg8 93. Qg6+ Kh8 94. Qh5+ Kg8 95. Qg4+ Kh8 96. Qh3+ Kg8 97. Qg2+ Kh8 98. Qh1+ Kg8 99. Qg1+ Kh8 100. Qh2+ Kg8 101. Qg3+ Kh8 102. Qh4+ Kg8 103. Qg5+ Kh8 104. Qh6+ Kg8 105. Rg7+ Kf8 106. Qf6+ Ke8 107. Re7+ Kd8 108. Qd6+ Kc8 109. Rc7+ Kb8 110. Qb6+ Ka8 111. Qc6+ Kb8 112. Rb7+ Ka8 113. Rxb5+ Ka7 114. Rb7+ Ka8 115. Rc7+ Kb8 116. Qb6+ Ka8 117. Qa5+ Kb8 118. Qb5+ Ka8 119. Qa6+ Kb8 120. Rb7+ Kc8 121. Qc6+ Kd8 122. Rd7+ Ke8 123. Qe6+ Kf8 124. Rf7+ Kg8 125. Qg6+ Kh8 126. Qh5+ Kg8 127. Qg4+ Kh8 128. Qh3+ Kg8 129. Qg2+ Kh8 130. Qh1+ Kg8 131. Qg1+ Kh8 132. Qh2+ Kg8 133. Qg3+ Kh8 134. Qh4+ Kg8 135. Qg5+ Kh8 136. Qf6+ Kg8 137. Rg7+ Kh8 138. Rg6+ Kh7 139. Qf7+ Kh8 140. Qe8+ Kh7 141. Qd7+ Kh8 142. Qc8+ Kh7 143. Qb7+ Kh8 144. Qa8+ Kh7 145. Qa7+ Kh8 146. Qb8+ Kh7 147. Qc7+ Kh8 148. Qd8+ Kh7 149. Qe7+ Kh8 150. Qf8+ Kh7 151. Rg7+ Kh6 152. Qf6+ Kh5 153. Rg5+ Kh4 154. Qf4+ Kh3 155. Rg3+ Kh2 156. Qf2+ Kh1 157. Qf3+ Kh2 158. Rg2+ Kh1 159. Rxd2+ Kg1 160. Rg2+ Kh1 161. Rg3+ Kh2 162. Qf2+ Kh1 163. Qe1+ Kh2 164. Qe2+ Kh1 165. Qf1+ Kh2 166. Rg2+ Kh3 167. Qf3+ Kh4 168. Rg4+ Kh5 169. Qf5+ Kh6 170. Rg6+ Kh7 171. Qf7+ Kh8 172. Qf6+ Kh7 173. Rg7+ Kh8 174. Rf7+ Kg8 175. Qg6+ Kh8 176. Qh5+ Kg8 177. Qg4+ Kh8 178. Qh3+ Kg8 179. Qg2+ Kh8 180. Qh1+ Kg8 181. Qg1+ Kh8 182. Qh2+ Kg8 183. Qg3+ Kh8 184. Qh4+ Kg8 185. Qg5+ Kh8 186. Qh6+ Kg8 187. Rg7+ Kf8 188. Qf6+ Ke8 189. Re7+ Kd8 190. Qd6+ Kc8 191. Rc7+ Kb8 192. Qb6+ Ka8 193. Qc6+ Kb8 194. Rb7+ Ka8 195. Rxb4+ Ka7 196. Rb7+ Ka8 197. Rc7+ Kb8 198. Qb6+ Ka8 199. Qa5+ Kb8 200. Qb5+ Ka8 201. Qa6+ Kb8 202. Rb7+ Kc8 203. Qc6+ Kd8 204. Rd7+ Ke8 205. Qe6+ Kf8 206. Rf7+ Kg8 207. Qg6+ Kh8 208. Qh5+ Kg8 209. Qg4+ Kh8 210. Qh3+ Kg8 211. Qg2+ Kh8 212. Qh1+ Kg8 213. Qg1+ Kh8 214. Qh2+ Kg8 215. Qg3+ Kh8 216. Qh4+ Kg8 217. Qg5+ Kh8 218. Qf6+ Kg8 219. Rg7+ Kh8 220. Rg6+ Kh7 221. Qf7+ Kh8 222. Qe8+ Kh7 223. Qd7+ Kh8 224. Qc8+ Kh7 225. Qb7+ Kh8 226. Qa8+ Kh7 227. Qa7+ Kh8 228. Qb8+ Kh7 229. Qc7+ Kh8 230. Qd8+ Kh7 231. Qe7+ Kh8 232. Qf8+ Kh7 233. Rg7+ Kh6 234. Qf6+ Kh5 235. Rg5+ Kh4 236. Qf4+ Kh3 237. Rg3+ Kh2 238. Qf2+ Kh1 239. Qf3+ Kh2 240. Rg2+ Kh1 241. Rxc2+ Kg1 242. Rg2+ Kh1 243. Rg3+ Kh2 244. Qf2+ Kh1 245. Qe1+ Kh2 246. Qe2+ Kh1 247. Qf1+ Kh2 248. Rg2+ Kh3 249. Qf3+ Kh4 250. Rg4+ Kh5 251. Qf5+ Kh6 252. Rg6+ Kh7 253. Qf7+ Kh8 254. Qe8+ Kh7 255. Qd7+ Kh8 256. Qc8+ Kh7 257. Qb7+ Kh8 258. Qa8+ Kh7 259. Qa7+ Kh8 260. Qb8+ Kh7 261. Qc7+ Kh8 262. Qd8+ Kh7 263. Qe7+ Kh8 264. Qf8+ Kh7 265. Rg7+ Kh6 266. Qf6+ Kh5 267. Rg5+ Kh4 268. Qf4+ Kh3 269. Rg3+ Kh2 270. Qf2+ Kh1 271. Qf3+ Kh2 272. Rg2+ Kh1 273. Rxb2+ Kg1 274. Rg2+ Kh1 275. Rg3+ Kh2 276. Qf2+ Kh1 277. Qe1+ Kh2 278. Qd2+ Kh1 279. Qd1+ Kh2 280. Qe2+ Kh1 281. Qf1+ Kh2 282. Rg2+ Kh3 283. Qf3+ Kh4 284. Rg4+ Kh5 285. Qf5+ Kh6 286. Rg6+ Kh7 287. Qf7+ Kh8 288. Qf6+ Kh7 289. Rg7+ Kh8 290. Rf7+ Kg8 291. Qg5+ Kh8 292. Qh4+ Kg8 293. Qg3+ Kh8 294. Qh2+ Kg8 295. Qg1+ Kh8 296. Qh1+ Kg8 297. Qg2+ Kh8 298. Qh3+ Kg8 299. Qg4+ Kh8 300. Qh5+ Kg8 301. Qg6+ Kh8 302. Qh6+ Kg8 303. Rg7+ Kf8 304. Qf6+ Ke8 305. Re7+ Kd8 306. Qd6+ Kc8 307. Rc7+ Kb8 308. Qb6+ Ka8 309. Qc6+ Kb8 310. Rb7+ Ka8 311. Rxb3+ Ka7 312. Rb7+ Ka8 313. Rc7+ Kb8 314. Qb6+ Ka8 315. Qa5+ Kb8 316. Qb5+ Ka8 317. Qa6+ Kb8 318. Rb7+ Kc8 319. Qc6+ Kd8 320. Rd7+ Ke8 321. Qe6+ Kf8 322. Rf7+ Kg8 323. Qg6+ Kh8 324. Qf6+ Kg8 325. Rg7+ Kh8 326. Rg6+ Kh7 327. Qf7+ Kh8 328. Qe8+ Kh7 329. Qd7+ Kh8 330. Qc8+ Kh7 331. Qb7+ Kh8 332. Qa8+ Kh7 333. Qa7+ Kh8 334. Qb8+ Kh7 335. Qc7+ Kh8 336. Qd8+ Kh7 337. Qe7+ Kh8 338. Qf8+ Kh7 339. Rg7+ Kh6 340. Qf6+ Kh5 341. Rg5+ Kh4 342. Qf4+ Kh3 343. Rg3+ Kh2 344. Qf2+ Kh1 345. Qf3+ Kh2 346. Rg2+ Kh1 347. Rxa2+ Kg1 348. Rg2+ Kh1 349. Rg3+ Kh2 350. Qf2+ Kh1 351. Qe1+ Kh2 352. Qd2+ Kh1 353. Qd1+ Kh2 354. Qe2+ Kh1 355. Qf1+ Kh2 356. Rg2+ Kh3 357. Qf3+ Kh4 358. Rg4+ Kh5 359. Qf5+ Kh6 360. Rg6+ Kh7 361. Qf7+ Kh8 362. Qf6+ Kh7 363. Rg7+ Kh8 364. Rf7+ Kg8 365. Qg6+ Kh8 366. Qh5+ Kg8 367. Qg4+ Kh8 368. Qh3+ Kg8 369. Qg2+ Kh8 370. Qh1+ Kg8 371. Qg1+ Kh8 372. Qh2+ Kg8 373. Qg3+ Kh8 374. Qh4+ Kg8 375. Qg5+ Kh8 376. Qh6+ Kg8 377. Rg7+ Kf8 378. Qf6+ Ke8 379. Re7+ Kd8 380. Qd6+ Kc8 381. Rc7+ Kb8 382. Qb6+ Ka8 383. Qa5+ Kb8 384. Qb4+ Ka8 385. Qa3+ Kb8 386. Qb3+ Ka8 387. Qa4+ Kb8 388. Qb5+ Ka8 389. Qa6+ Kb8 390. Qb6+ Ka8 391. Qc6+ Kb8 392. Rb7+ Ka8 393. Rxb1+ Ka7 394. Rb7+ Ka8 395. Rc7+ Kb8 396. Qb6+ Ka8 397. Qa5+ Kb8 398. Qb4+ Ka8 399. Qa3+ Kb8 400. Qb2+ Ka8 401. Qa1+ Kb8 402. Qb1+ Ka8 403. Qa2+ Kb8 404. Qb3+ Ka8 405. Qa4+ Kb8 406. Qb5+ Ka8 407. Qa6+ Kb8 408. Rb7+ Kc8 409. Qc6+ Kd8 410. Rd7+ Ke8 411. Qe6+ Kf8 412. Rf7+ Kg8 413. Qg6+ Kh8 414. Qf6+ Kg8 415. Rg7+ Kh8 416. Rg6+ Kh7 417. Qf7+ Kh8 418. Qe8+ Kh7 419. Qd7+ Kh8 420. Qc8+ Kh7 421. Qb7+ Kh8 422. Qa8+ Kh7 423. Qa7+ Kh8 424. Qb8+ Kh7 425. Qc7+ Kh8 426. Qd8+ Kh7 427. Qe7+ Kh8 428. Qf8+ Kh7 429. Rg7+ Kh6 430. Qf6+ Kh5 431. Rg5+ Kh4 432. Qf4+ Kh3 433. Rg3+ Kh2 434. Qf2+ Kh1 435. Qf3+ Kh2 436. Qf2+ Kh1 437. Qe1+ Kh2 438. Qd2+ Kh1 439. Qc1+ Kh2 440. Qb2+ Kh1 441. Qa1+ Kh2 442. Qa2+ Kh1 443. Qb1+ Kh2 444. Qc2+ Kh1 445. Qd1+ Kh2 446. Qe2+ Kh1 447. Qf3+ Kh2 448. Rg2+ Kh1 449. Rf2+ Kg1 450. Qg4+ Kh1 451. Qh5+ Kg1 452. Qg6+ Kh1 453. Qh7+ Kg1 454. Qg8+ Kh1 455. Qh8+ Kg1 456. Qg7+ Kh1 457. Qh6+ Kg1 458. Qg5+ Kh1 459. Ng3+ Kg1 460. Nh1+ Kxh1 461. Qh4+ Kg1 462. Qg3+ Kh1 463. Qh3+ Kg1 464. Rg2+ Kf1 465. Qf3+ Ke1 466. Re2+ Kd1 467. Qd3+ Kc1 468. Rc2+ Kb1 469. Qb3+ Ka1 470. Qc3+ Kb1 471. Rb2+ Ka1 472. Rb3+ Ka2 473. Qc2+ Ka1 474. Qc1+ Ka2 475. Rb2+ Ka3 476. Qc3+ Ka4 477. Rb4+ Ka5 478. Qc5+ Ka6 479. Rb6+ Ka7 480. Qc7+ Ka8 481. Qd8+ Ka7 482. Qe7+ Ka8 483. Qf8+ Ka7 484. Qg7+ Ka8 485. Qh8+ Ka7 486. Qh7+ Ka8 487. Qg8+ Ka7 488. Qf7+ Ka8 489. Qe8+ Ka7 490. Qd7+ Ka8 491. Qc6+ Ka7 492. Rb7+ Ka8 493. Rc7+ Kb8 494. Qb6+ Ka8 495. Qa5+ Kb8 496. Qb4+ Ka8 497. Qa3+ Kb8 498. Qb2+ Ka8 499. Qa1+ Kb8 500. Qb1+ Ka8 501. Qa2+ Kb8 502. Qb3+ Ka8 503. Qa4+ Kb8 504. Qb5+ Ka8 505. Qa6+ Kb8 506. Rb7+ Kc8 507. Qc6+ Kd8 508. Rd7+ Ke8 509. Qe6+ Kf8 510. Rf7+ Kg8 511. Qg6+ Kh8 512. Qh5+ Kg8 513. Qg4+ Kh8 514. Qh3+ Kg8 515. Qg2+ Kh8 516. Qh1+ Kg8 517. Qg1+ Kh8 518. Qh2+ Kg8 519. Qg3+ Kh8 520. Qh4+ Kg8 521. Qg5+ Kh8 522. Ng6+ Kg8 523. Nh8+ Kxh8 524. Qf6+ Kg8 525. Rg7+ Kh8 526. Rg6+ Kh7 527. Qf7+ Kh8 528. Qf8+ Kh7 529. Rg7+ Kh6 530. Qf6+ Kh5 531. Rg5+ Kh4 532. Qf4+ Kh3 533. Rg3+ Kh2 534. Qf2+ Kh1 535. Qf3+ Kh2 536. Rg2+ Kh1 537. Rf2+ Kg1 538. Qg3+ Kh1 539. Qh3+ Kg1 540. Rg2+ Kf1 541. Qf3+ Ke1 542. Re2+ Kd1 543. Qd3+ Kc1 544. Rc2+ Kb1 545. Qb3+ Ka1 546. Qc3+ Kb1 547. Rb2+ Ka1 548. Rb3+ Ka2 549. Qc2+ Ka1 550. Qc1+ Ka2 551. Rb2+ Ka3 552. Qc3+ Ka4 553. Rb4+ Ka5 554. Qc5+ Ka6 555. Rb6+ Ka7 556. Qc7+ Ka8 557. Qd8+ Ka7 558. Qe7+ Ka8 559. Qf8+ Ka7 560. Qg7+ Ka8 561. Qh8+ Ka7 562. Qh7+ Ka8 563. Qg8+ Ka7 564. Qf7+ Ka8 565. Qe8+ Ka7 566. Qd7+ Ka8 567. Nc7+ Ka7 568. Na8+ Kxa8 569. Qc6+ Ka7 570. Rb7+ Ka8 571. Rc7+ Kb8 572. Qb6+ Ka8 573. Qa6+ Kb8 574. Rb7+ Kc8 575. Qc6+ Kd8 576. Rd7+ Ke8 577. Qe6+ Kf8 578. Rf7+ Kg8 579. Qg6+ Kh8 580. Qf6+ Kg8 581. Rg7+ Kh8 582. Rg6+ Kh7 583. Qf7+ Kh8 584. Qf8+ Kh7 585. Rg7+ Kh6 586. Qf6+ Kh5 587. Rg5+ Kh4 588. Qf4+ Kh3 589. Rg3+ Kh2 590. Qf2+ Kh1 591. Qf3+ Kh2 592. Rg2+ Kh1 593. Rf2+ Kg1 594. Qg3+ Kh1 595. Qh3+ Kg1 596. Rg2+ Kf1 597. Qf3+ Ke1 598. Re2+ Kd1 599. Qd3+ Kc1 600. Rc2+ Kb1 601. Qb3+ Ka1 602. Qc3+ Kb1 603. Rb2+ Ka1 604. Rb3+ Ka2 605. Qc2+ Ka1 606. Qc1+ Ka2 607. Rb2+ Ka3 608. Qc3+ Ka4 609. Rb4+ Ka5 610. Qc5+ Ka6 611. Rb6+ Ka7 612. Qc7+ Ka8 613. Qc6+ Ka7 614. Ra6+ Kb8 615. Qb6+ Kc8 616. Ra8+ Kd7 617. Rd8+ Ke7 618. Qd6+ Kf7 619. Rf8+ Kg7 620. Qf6+ Kh7 621. Qh8+ Kg6 622. Rf6+ Kg5 623. Qh6+ Kg4 624. Rf4+ Kg3 625. Qh4+ Kg2 626. Rf2+ Kg1 627. Qh2#
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  • 1
    LOL, this immediately brings to mind the "Linkes gegen Rechtes Alsterufer" incident where one kiddie tried to mate another one. Used three queens, just to be safe, and always found the check that didn't mate. After more than 10 checks, he had a flash of ingenuity and instead cut off instead of checking. With immediate stalemate, naturally...
    – Hauke Reddmann
    Mar 7 at 7:53
  • 1
    Great! I understand that you can't add another White unit because bP's captured 12. At the end you can extend the chase a bit further starting with with 274 Rf1+ 275 Qf2+ 276 Rh1+ 277 Rh4+ 278 Qf4+ 279 Rh6+ 280 Qf6+ 281 Qh8+ 282 Rf6+ etc.
    – Noam D. Elkies
    Mar 7 at 17:57
  • @NoamD.Elkies Thanks for that! And it actually is possible to add more white units, e.g 8/8/p7/1p2K3/1p2P3/1p2P3/nnpbp1R1/1b3Qrk w - - 0 1, but there is no point in doing so, atm, as I have been unable to find a way to add another capturing roundabout for White, due to bPe2 guarding f1. Adding pieces for a technical one or two moves will not come until this matrix is exhausted. Any ideas are welcome.
    – Rewan Demontay
    Mar 7 at 22:16
  • 2
    Yes, I can believe that this is even longer than that I suggested. But it's not yet wrung [sic] dry: at the end, instead of proceeding with 459 Qh4+ Kg1 460 Qg3+ etc. you can interpolate 459 Ng3+ Kh1 460 Nh1+ Kxh1 -- and now without the Ne4 we can take the bK on another round trip. Better yet, make it a 3/4 round trip to h8 and play the same trick with the Ne5, then again to a8 and jettison the Nd5, then a last round trip before finally mating with Q+R vs. K.
    – Noam D. Elkies
    Mar 8 at 4:29
  • 2
    @NoamD.Elkies With this extra roundabout, and the chase extension, 627. Do you see any more wrginges?
    – Rewan Demontay
    Mar 9 at 7:47

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