size(0,10cm); import graph;  int dx = 4, dy = 3;  void interSphere(pair[] c1, pair[] c2) {     pen whitepen = defaultpen + white + 4*linewidth(defaultpen);     for(int i = 0; i < c1.length; ++i) {         for(int j = 0; j < c2.length; ++j) {             pair delta = 1.1*unit(c2[j]-c1[i]);             draw(c1[i]+delta--c2[j]-delta, whitepen);             draw(c1[i]+delta--c2[j]-delta, Arrow);         }     } }  void unitCircs(pair[] c0, pen p = defaultpen) {     for(int i = 0; i < c0.length; ++i) {         draw(Circle(c0[i], 1), p);     } }  pair[] c0 = {(0, 0), (0, dy), (0, 2*dy)},        c1 = {(dx, -1.5), (dx, -1.5 + dy), (dx, -1.5 + 2*dy), (dx, -1.5+3*dy)},        c2 = {(2*dx, -1.5 + dy), (2*dx, -1.5 + 2*dy)};  pen redPen = defaultpen + heavyred,     bluePen = defaultpen + heavyblue,     greenPen = defaultpen + deepgreen; unitCircs(c0, redPen); unitCircs(c1, bluePen); unitCircs(c2, greenPen);  interSphere(c0, c1); interSphere(c1, c2);  label("Input", (0, 2*dy + 1), N, redPen); label("Hidden", (dx, -1.5 + 3dy + 1), N, bluePen); label("Output", (2*dx, -1.5 + 2dy + 1), N, greenPen);  real rbox = 2*dx + 1.025; draw((rbox,-3)--(rbox, 3), invisible);