I'm currently using the TheoryOfComputation book by Maheshwari and Smid to study regular expressions. In the book, examples were given as:
The language
$$\{w \in \{0,1\}^* : \text{the length of } w \text{ is even}\}$$
is described by the regular expression
$$((0 ∪ 1)(0 ∪ 1))^*$$
Some people in class said that it can also be written as
$$((0 + 1)(0 + 1))^*$$
Is this true?
Yes. $+$ and $\cup$ both denote the union operation.