Question: How can I create a superscipcted variable in 1-D math?

Dear all,
I want to create a superscripted and subscripted variable in 1-D math. I know that I can establish a subscripted variable by using double “_”, for example, the execution of the following command causes assignment 2 to u__b, in which b is the subscript of u.
However, I don’t know any way to create either a superscripted variable or a variable having both the subscript and superscript in 1-D math.
Can anyone help me?
 Best wishes

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