Mr. Baker, Mr. Pastry, and Mr. Florist are three friends who each have a different profession among the following: baker, pastry chef, and florist. However, each of them does not necessarily practice the profession corresponding to their name. Among the following information, only one is true:

- Mr. Pastry is not a baker.
- Mr. Florist is not a pastry chef.
- Mr. Pastry is a pastry chef.
- Mr. Florist is not a baker.

Question: What are the professions practiced by the 3 friends?
Let's study the four cases:

1st case: The first proposition is true. Then, Mr. Pastry is not a baker and the other propositions are false, so Mr. Florist is a pastry chef (from the false proposition 2) and a baker (from the false proposition 4): this is impossible because each protagonist practices only one profession.

2nd case: Mr. Florist is not a pastry chef. Therefore, Mr. Pastry is a baker (from the first proposition which is false) and Mr. Florist is also a baker (from the 4th proposition which is false). This is impossible because the three protagonists practice different professions.

3rd case: Mr. Pastry is a pastry chef. Therefore, the first proposition is false, so Mr. Pastry practices two professions, which is impossible.

4th case: Mr. Florist is not a baker. From propositions 1 and 2 (which are false), we deduce that: Mr. Pastry is a baker and Mr. Florist is a pastry chef. Point 3 does not contradict what precedes. Finally, Mr. Baker is a florist.

The fourth case is the only possible one, so the professions of the three protagonists are those stated in the last case.