BlockList : Block BlockList 
  | 
  ;

  Block : simb N DList 
  ;

  DList : 
  | Deriv DList 
  ;

  Deriv : id SimbList 
  ;

  SimbList : 
  | Simb SimbList 
  ;

  Simb : simb T 
  | simb NT 
  ;

/* --- BlockList ---*/
typedef struct sBlockList 
{ int flag;
  union {  
    struct {
        Block s1;

        BlockList s2;

      } d1;
    struct {
      } d2;

  } u;
} *BlockList;

/* --- Block ---*/
typedef struct sBlock 
{ int flag;
  union {  
    struct {
        simb s1;

        N s2;

        DList s3;

      } d1;

  } u;
} *Block;

/* --- DList ---*/
typedef struct sDList 
{ int flag;
  union {  
    struct {
      } d1;
    struct {
        Deriv s1;

        DList s2;

      } d2;

  } u;
} *DList;

/* --- Deriv ---*/
typedef struct sDeriv 
{ int flag;
  union {  
    struct {
        id s1;

        SimbList s2;

      } d1;

  } u;
} *Deriv;

/* --- SimbList ---*/
typedef struct sSimbList 
{ int flag;
  union {  
    struct {
      } d1;
    struct {
        Simb s1;

        SimbList s2;

      } d2;

  } u;
} *SimbList;

/* --- Simb ---*/
typedef struct sSimb 
{ int flag;
  union {  
    struct {
        simb s1;

        T s2;

      } d1;
    struct {
        simb s1;

        NT s2;

      } d2;

  } u;
} *Simb;