m4_define(memoed, `$1() {return("$1" in Memo?Memo["$1"]:Memo["$1"]=_memoed_$1() )} function _memoed_$1()')

 function model() { return x() - 1/x() }

 function memoed(x)  { return normal(10,4)  }

 function normal(m,s) { return m+box_muller()*s; }

 function box_muller(m,s,    n,x1,x2,w) {
   w=1;
   while (w >= 1) {
     x1= 2.0 * rand() - 1;
     x2= 2.0 * rand() - 1;
     w = x1*x1 + x2*x2};
   w = sqrt((-2.0 * log(w))/w);
   return x1 * w;
 }