Numerical Solution of Multiple Nonlinear Volterra Integral Equations
  We analyze a discretization method for solving nonlinear integral equations that contain multiple integrals. These equations include integral equations with a Volterra series, instead of a single integral term, on one side of the equation. We prove existence and uniqueness of solutions, and convergence and estimates of the order of convergence for the numerical methods of solution. 
S. A. Belbas, Yuriy Bulka