... precept¹

That is a kind of definition that prescribes ``what you are to do in order to gain perceptual acquaintance with the object of the world'' (Peirce, 1958, CP, 2.330).

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... structures).²

The epistemic and cognitive role of mirror and unveiling diagrams in the discovery of non-Euclidean geometry is illustrated in (Magnani, 2002).

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... (1966).³

For an easy introduction to non-standard calculus see (Keisler, 1976a, 1976b).

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