Here's my question:

Attempt:

So the set of theorems is .

- The only axiom is .

- The alphabet is

- Rules of inference (here and represent any string, possibly empty, of symbols from the alphabet):
For example is a theorem of this system. To see this, we provide the following derivation:

- From infer
- From xyx infer xBx

1. (Axiom)

2. (From 1 by rule 1)

3. (From 2 by rule 1)

4. (From 3 by rule 2)

Is this correct?