function   RR=checkchildren(j,RR)

% if a symbol 't' is encounted, then make all its descendants in reference  

% matrix RR's components equal 1---ZEROTREES



global N

[m,n]=size(N);



for i=(4*j-3):4*j;

      if  i<=m, 

             

         RR(N(i,1),N(i,2))=1;

           

         RR=checkchildren(i,RR);

     

     end

    

       

end;