Theory related to **ExprTuple** types of Prove-It expressions. An **ExprTuple** is an ordered sequence of expressions. It may contain an **ExprRange** that represents an indeterminant number of *elements* within the sequence. For example, $(a, b_1, \ldots, b_n, c)$ is a tuple of $n+2$ elements with $b_1, \ldots, b_n$ as an **ExprRange** that is a single entry of this tuple. Each *entry* of the **ExprTuple** is a single **Expression** which may represent zero or more elements of the tuple sequence.

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```
import proveit
%theory # toggles between interactive and static modes
```