$\forall$$k$, $b$:$\mathbb{N}$, $f$:($\mathbb{N}$$_{\mbox{\scriptsize $<$$k$}}$$\rightarrow\mathbb{Z}$). ($\forall$$x$:$\mathbb{N}$$_{\mbox{\scriptsize $<$$k$}}$. $f$($x$)$\leq$$b$) $\Rightarrow$ sum($f$($x$) $\mid$ $x$ $<$ $k$)$\leq$$b$$\cdot$$k$