  We study perturbations of functions $f(A,B)$ of noncommuting self-adjoint
operators $A$ and $B$ that can be defined in terms of double operator
integrals. We prove that if $f$ belongs to the Besov class $B_{\be,1}^1(\R^2)$,
then we have the following Lipschitz type estimate in the Schatten--von Neumann
norm $\bS_p$, $1\le p\le2$ norm:
$\|f(A_1,B_1)-f(A_2,B_2)\|_{\bS_p}\le\const(\|A_1-A_2\|_{\bS_p}+\|B_1-B_2\|_{\bS_p})$.
However, the condition $f\in B_{\be,1}^1(\R^2)$ does not imply the Lipschitz
type estimate in $\bS_p$ with $p>2$. The main tool is Schatten--von Neumann
norm estimates for triple operator integrals.
