1 + (1 + (1 + 1)) = (1 + (1 + 1)) + 1
(1 + 1) + (1 + 1) = ((1 + 1) + 1) + 1
Wie beweist man das?

(1 + 1) + (1 + (1 + 1)) = ((1 + 1) + 1) + (1 + 1) =
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