Cauchy's Mean Theorem/Proof 3

Proof
For $p \in \R$, let $\map {M_p} {x_1, x_2, \ldots, x_n}$ denote the Hölder mean with exponent $p$ of $x_1, x_2, \ldots, x_n$.

By definition of Hölder Mean with $p = 0$:
 * $\map {M_0} {x_1, x_2, \ldots, x_n} = \map G {x_1, x_2, \ldots, x_n}$

From Hölder Mean for Exponent 1 is Arithmetic Mean:
 * $\map {M_1} {x_1, x_2, \ldots, x_n} = \map G {x_1, x_2, \ldots, x_n}$

The result follows from Inequality of Hölder Means:
 * $0 < 1 \implies \map {M_0} {x_1, x_2, \ldots, x_n} < \map {M_1} {x_1, x_2, \ldots, x_n}$

unless $x_1 = x_2 = \cdots = x_n$, in which case:
 * $\map {M_0} {x_1, x_2, \ldots, x_n} = \map {M_1} {x_1, x_2, \ldots, x_n}$

Hence the result.