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Answer: To write a function that cannot change the value of its argument, you can use the concept of immutability. This can be achieved with the following steps: 1. Understand immutability: Immutability refers to the quality of an object whose state cannot be modified after it is created. 2. Consider pass by value or pass by reference: In pass by value, the function cannot change the original value, while in pass by reference, the function can modify the value indirectly. 3. Use different approaches to ensure immutability such as using immutable data types, creating a copy of the object before passing it to the function, or specifying that a function should not modify its arguments (e.g., `const` keyword in C++). 4. In languages like Python, using immutable objects such as strings, integers, and floats ensures that the function cannot change their values.