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You are talking about $B^{0,\infty}_\infty$.

Take a function $u$ in the Zygmund class $B^{1,\infty}_\infty$, which the vector space of $L^\infty$ functions such that $$\exists C,\forall x,h,\quad \vert(u(x+h)+u(x-h)-2u(x)\vert\le C\vert h\vert. $$

Note that $B^{1,\infty}_\infty\supset L^\infty\cap \text{Lipschitz}$. text{Lipschitz}$ (here Lipschitz means $\exists C,\forall x,h,\quad \vert(u(x+h)-u(x)\vert\le C\vert h\vert $).

Now the derivative of $u$ belongs to $B^{0,\infty}_\infty$.

In particular, first derivatives of functions in $L^\infty\cap \text{Lipschitz}$ belong to $B^{0,\infty}_\infty$.

show/hide this revision's text 1

You are talking about $B^{0,\infty}_\infty$.

Take a function $u$ in the Zygmund class $B^{1,\infty}_\infty$, which the vector space of $L^\infty$ functions such that $$\exists C,\forall x,h,\quad \vert(u(x+h)+u(x-h)-2u(x)\vert\le C\vert h\vert. $$

Note that $B^{1,\infty}_\infty\supset L^\infty\cap \text{Lipschitz}$.

Now the derivative of $u$ belongs to $B^{0,\infty}_\infty$.

In particular, derivatives of functions in $L^\infty\cap \text{Lipschitz}$ belong to $B^{0,\infty}_\infty$.