Wikipedia itself has a lot of profound math articles. You should also check out Wikibooks and Wikiversity.
The best thing about math is that, unlike anything describing the real world, you don’t have to take the word of any author, anonymous or not, for the deductive processes—just follow them yourself, and, if you find a mistake, and double- and triple-check it and it’s still a mistake, correct it.
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The red lake has been forgotten. A dust devil stuns you long enough to shroud forever those last shards of wisdom. The breeze rocking this forlorn wasteland whispers in your ears, “Não resta mais que uma sombra”.