Even though the matrix is infinitely large, we conjecture from all observed numerical calculations that the positive elements k j+1,j converge in the sense that |k j+1,j 2k j+2,j+1 |R0 as jR'. Therefore, for numerical evaluation we 'closed' the matrix to an (n+1) 2 matrix with k nn = k n+1,n . For the four special cases, R q could be calculated numerically in MathematicaH, but for other cases considered, the entries of the matrix had to be determined by numerical simulation. Analysis of single-step tracing with delay could be done by calculating R from the next-generation matrix, as for the model without delay (see Supporting Information for all details).