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\[ \Delta_0^1 A = \int_{\lambda=0}^{\lambda=1} \left( \frac{\partial
    A(\lambda)}{\partial\lambda} \right)_\lambda \mathrm{d}\lambda
\approx \sum_{i=0}^{n-1} w_i \frac{A(\lambda_{i} + \delta) -
  A(\lambda_i)}{\delta} \]

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