Determine if each function is one-one.
To each country in the world which has a prime minister assign its prime minister.

Answer

To determine if the function described is one-one, we need to analyze the relationship between the countries and their prime ministers.

### Step-by-Step Solution:

1. **Define the Sets**:
- Let set A be the set of countries in the world that have a prime minister.
- Let set B be the set of prime ministers of these countries.

2. **Understand the Function**:
- The function assigns each country (from set A) to its prime minister (in set B). This means that for every country, there is a specific prime minister associated with it.

3. **Check for One-One Function**:
- A function is called one-one (or injective) if different elements in set A map to different elements in set B. In other words, if country X has prime minister P1 and country Y has prime minister P2, then if X ≠ Y, it must be true that P1 ≠ P2.

4. **Analyze the Mapping**:
- Since each country has its own unique prime minister, no two different countries can have the same prime minister. For example, if Country A has Prime Minister A1, and Country B has Prime Minister B1, then A1 cannot be equal to B1 if A ≠ B.

5. **Conclusion**:
- Since every country with a prime minister has a unique prime minister, we can conclude that the function is indeed one-one.

### Final Answer:
Yes, the function that assigns each country in the world which has a prime minister to its prime minister is a one-one function.

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