FWIW, I wrote "I'm in mensa" not to brag so much as ... I got in through test scores, and (obviously) have some raw measure of ability in cognitive areas, but still wasn't able to immediately get that algorithm from the english. I get what it means, and understand the implications of the algorithm, but couldn't make that immediate jump. The older I get, the harder it is for me to tell when someone is sharp and maybe just can't grasp something immediately, and when they truly can't get it. I probably make more allowances than I did in my youth, precisely because I know my own shortcomings more now than 20 years ago.