grammar simplif{

     terminal a,b,d;
     nonterminal S,B,A,C,D;
     axiom S;

     productions{
          S:=A a| B | D;
          B:=b;
          A:=a A| b A | B;
          C:= a b d;
     }
}

/*
ENG: We are going to eliminate the productions of the grammar
     that don't derivate in terminal strings. In this case
     the production [S:=D] will be removed.
ESP: Es una gramatica a la que vamos a eliminar las producciones
     que no derivan en cadenas de terminales en este caso se
     eliminara la produccion [S:=D].
*/

print(simplif);
gramsimplificad = remnongen(simplif);