 ring r=(0,t),(x,y),dp;
matrix m[5][6]=x,y,1,2,0,x+y;
defined(mm);
==> 0
defined(r) and defined(m);
==> 1
defined(m)==voice; // m is defined in the current level
==> 1
defined(x);
==> 1
defined(z);
==> 0
defined("z");
==> 1
defined(t);
==> 1
defined(42);
==> 1
