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"The modern era in homotopy theory began in the 1960s with the profound realization, first codified by Boardman in his construction of the stable category, that the category of spaces up to stable homotopy equivalence is equipped with a rich algebraic structure, formally similar to the derived category of a commutative ring R. For example, for pointed spaces the natural map from the categorical co-product to the categorical product becomes more and more connected as the pieces themselves become more and more connected"--