picoeva

      `Added for nondeterministic computing`
      eval_amb(Exp):=
        call(
          { tbl: Exp[AMB_TAB_idx];
            tab: tbl[TAB_TAB_idx];
            siz: size(tab);
            ctr: Exp[AMB_CTR_idx];
            if(siz=0
               continue(cont, AFS()),
               if(ctr > siz,
                  continue(cont, AFS()),
                  continue(cont, eval(tab[ctr])))) };