Kreweras considered the problem of counting noncrossing partitions of the set {1, 2,..., n}, whose elements are arranged into a cycle in its natural order, into p parts of given sizes n1, n2, ⋯ , np ...

Schrodinger's equation is usually treated as a postulate, and IMHO that's the best approach, rather than some kind of derivation based on chronologically earlier, but less general, principles and ...

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