In Debreu's 1954 ordinal utility representation theorem, the utility is unique up to a positive monotonic transformation.

While the uniqueness result is well-known, I fail to find a proper reference. Debreu's original paper does not contain that uniqueness result.

Is there a good reference? Who was the first research find this uniquness result?

In Debreu's 1954 ordinal utility representation theorem, the utility is unique up to a positive monotonic transformation.

While the uniqueness result is well-known, I fail to find a proper reference. Debreu's original paper does not contain that uniqueness result.

Is there a good reference? Who was the first researcher find this uniqueness result?