Hi! I'm happy to help you with your question.
a. C type declarations for the abstract syntax tree structure for the grammar:
```c
typedef enum { ATOM_NUMBER, ATOM_IDENTIFIER } AtomType;
typedef struct Atom {
AtomType type;
union {
int number;
char *identifier;
} value;
} Atom;
typedef struct LExp {
enum { ATOM_NODE, LIST_NODE } type;
union {
Atom atom;
struct LExpSeq *list;
} value;
} LExp;
typedef struct LExpSeq {
LExp *lexp;
struct LExpSeq *next;
} LExpSeq;
```
b. EBNF translation of the grammar:
```
lexp = atom | list ;
atom = number | identifier ;
list = "(", lexp-seq, ")" ;
lexp-seq = {lexp}, lexp ;
```
c. Unfortunately, I'm unable to draw syntax diagrams as a text-based AI. However, I can describe the process for you, and you can use an online tool or draw it manually.
1. Start with a rectangle for each non-terminal (lexp, atom, list, lexp-seq).
2. Connect each non-terminal to its respective production rules using arrows.
3. Use rounded rectangles for terminals (number, identifier, "(", ")").
4. For the "|" operator, draw two branches, one for each alternative.
5. For the "{}" operator, draw a loop from the start to the end of the repeated sequence.
I hope this helps! Let me know if you have any further questions.