Small step from Asperger's to there, and Bobby Fischer is revered.
Would " Rainman " be allowed to challenge for title?

If someone like "Rainman" would play against a strong grandmaster in a match, and he memorized a whole lot of opening books and endgame databases, couldn't the grandmaster opponent just get out of book relatively early and outplay him from then on?

I think you need to go and watch that movie again, then you might get the quote right.
Since chess has not been "solved", then I suspect even a "super-rainman" would not be able to simply rely on memory.

Yeah, but read up on the real rain man -- he has an IQ of like... 65. As soon as it left book he'd shake the guys hand and be happy with himself (no, seriously).
You're right, he could memorize MCO, 100,000 master games, and some endgame stuff, but not 100% of it, especially the endgame table base stuff, which is more like a warehouse full of phone books

lol, fair enough
If someone like "Rainman" would play against a strong grandmaster in a match, and he memorized a whole lot of opening books and endgame databases, couldn't the grandmaster opponent just get out of book relatively early and outplay him from then on?
The whole point of GM strength is that they have also memorized thousands upon thousands of positions and naturally know the planning and progression of each. I remember the general estimate of GM strength was about 100,000 positions. An autistic person capable of such advanced memory storage being good at chess has already been demonstrated in GM David Navara, or so I recall reading anyway.
Also I want to point out that Rainman was highly embelished for a movie, and his feats in that movie were greatly exaggerated as well. 'Normal' professional memory champions have demonstrated far better ability.
The movie is based on kim peek, who is actually MORE impressive than what the movie portrays him as. Look him up!!!

If someone like "Rainman" would play against a strong grandmaster in a match, and he memorized a whole lot of opening books and endgame databases, couldn't the grandmaster opponent just get out of book relatively early and outplay him from then on?
The whole point of GM strength is that they have also memorized thousands upon thousands of positions and naturally know the planning and progression of each. I remember the general estimate of GM strength was about 100,000 positions. An autistic person capable of such advanced memory storage being good at chess has already been demonstrated in GM David Navara, or so I recall reading anyway.
Also I want to point out that Rainman was highly embelished for a movie, and his feats in that movie were greatly exaggerated as well. 'Normal' professional memory champions have demonstrated far better ability.
The movie is based on kim peek, who is actually MORE impressive than what the movie portrays him as. Look him up!!!
Yeah... I haven't seen the movie, but I could hardly imagine it being exaggerated. The guy reads two pages at once, left page with left eye, and right page with right eye for pete's sake... and he memorized all the counties and zip codes in the united states (as well as tons of other stuff).
There's no way professional memory champs could do better, they showed scan of his brain, the stuff basically goes directly into his memory. They said everything he's ever read he's memorized... (although he can't use it much beyond reciting it).
IMO this isn't going to work. Consider this: his memory might be superhuman, but it's still not as good as a high-end computer. Given that even computers don't have seven-piece tablebases (i.e. trying to solve any position of seven pieces or more via brute-force memorization needs more memory than even a (current) computer can handle), it's not even going to be close to the level needed to defeat a world champion. Or Rybka, for that matter.
Alternatively, here's another way to show that simply having a massive database isn't enough: Take the largest chess database you can find of high-level games. "Play" it against Rybka (or your friendly neighbourhood World Champion, whichever is easier), i.e. just pick the move with the highest winning percentage in the database in response to each of your opponent's moves. Guess who wins?

The problem with the question is that Rainman in the movie is a fictional character. The question holds as much weight as the question whether Superman would be allowed to compete in powerlifting or not.

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Obviously someone that can memorize a phone directory in a couple of days could easily memorize all openings and all endgame tablebases as well as thousands of databases of master level games in a few months time. Just a thought.
I think this shows a pretty fundamental misunderstanding of the complexity and depth of the resources listed above, and probably of autism as well. Memorization of that amount of material is simply beyond the capacity of any human -- autistic or otherwise.
Would the World Chess Federation acknowledge and allow an autistic person ,comparable to the fictional portrayal of Raymond Babbit " Rainman " , a chance at the world title. Obviously someone that can memorize a phone directory in a couple of days could easily memorize all openings and all endgame tablebases as well as thousands of databases of master level games in a few months time. Just a thought.