 Symmetrized exponential-splitting defect identity

For bounded matrices, differentiating the symmetrized product gives $F^{\prime }-(A+B)F=\frac{1}{2}([e^{tB},A]e^{tA}+[e^{tA},B]e^{tB})$. The variation-of-constants formula turns this into an integral expression for $F-e^{t(A+B)}$. This retains the noncommutativity of the factors explicitly; cancellation of their leading opposite commutators explains why the averaged product is more accurate than either ordering alone.