-- counts divergence
{ mseq ←
    λz.
    {
      add ← λz0.λz1. (z0->1+z1->1, z0->2+z1->2);
      sq ← λz. {
        r ⟜ z->1;i ⟜ z->2;
        (r^2-i^2,2*r*i)
      };
      abs ← λz. {r ⟜ z->1; i ⟜ z->2; √(r^2+i^2)};
      abs'gen. (0.0,0.0) [add (sq x) z] 64
    };
  [(>4)@.mseq x]`{0} ((frange _2.5 1 700) [(x,y)]⊗ (frange _1 1 400))
}