TheoremBase

Natural Numbers and Factorials Read in the Reals: the Order Carries Over, One Is Least, and Factorials Are Positive, Recursive and Nondecreasing

Read in the real numbers, every natural number is at least 1, and the factorials are at least 1, hence nonzero, satisfy (k+1)! = (k+1) k!, and are nondecreasing.

Statement

In the setting of Routine Facts Used Without Citation: Arithmetic, Maps, Predicativity and Indices, an element nn of N0\mathbb{N}_{0} read in R\mathbb{R} denotes its image nRn_{\mathbb{R}}, as in Commutative Rings, Fields and Ordered Fields: Standard Notation (iv), and n!n! is the factorial of n∈N0n\in\mathbb{N}_{0}.

For all m,n∈N0m,n\in\mathbb{N}_{0} with m≤nm\le n in N0\mathbb{N}_{0}, m≤nm\le n in R\mathbb{R}.

For every n∈Nn\in\mathbb{N}, 1≤n1\le n in R\mathbb{R}.

For every k∈N0k\in\mathbb{N}_{0}, in R\mathbb{R}: 1≤k!1\le k!, so that 0<k!0<k! and k!≠0k!\neq0; (k+1)!=(k+1)⋅k!(k+1)!=(k+1)\cdot k!; and k!≤(k+1)!k!\le(k+1)!.

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