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