Answer:
No, it is not necessarily true that a == b if a + b == b + a.
The concatenation of two lists a and b is the operation of creating a new list by appending the elements of b to the end of a. For example, if a is the list [1, 2, 3] and b is the list [4, 5], then a + b is the list [1, 2, 3, 4, 5].
If a + b == b + a, it means that the order in which the lists are concatenated does not affect the resulting list. However, this does not necessarily mean that the lists a and b are equal.
For example, consider the lists a = [1, 2] and b = [3, 4]. The expression a + b == b + a is true because a + b and b + a both result in the list [1, 2, 3, 4]. However, a != b because a and b are different lists with different elements.
In general, two lists are equal if and only if they have the same elements in the same order. Concatenating two lists does not affect the elements or order of the original lists, so the equality of the concatenated lists does not necessarily imply the equality of the original lists.