Normal ordering in the shift algebra and the dual of Spivey's identity
Spivey's Bell number identity involving Stirling numbers of the second kind was derived by Spivey considering set partitions. Since its original derivation it has been derived (and generalized) by many authors using different techniques. In particular, Katriel gave a proof using normal ordering in the Weyl algebra. Mező derived the dual of Spivey's identitiy for factorials involving (unsigned) Stirling numbers of the first kind considering permutations and cycles. The latter identity has also been been derived (and generalized) in different fashions. What is lacking in literature is a proof using normal ordering in the spirit of Katriel's proof of Spivey's identity. In the present work, this gap is filled by providing a new proof of the dual of Spivey's identity using normal ordering in the shift algebra.