# Arithmetic

Checks if a progression is arithmetic or not. An arithmetic series is the sum of a sequence in which each term is computed from the previous one by adding (or subtracting) a constant :

#### arithmetic?(Progression)

Given a progression, returns a list. If the progression is not arithmetic, the list just contains an element: `false`. Else, the list has two elements: `true` and the value , following the notation above.

#### arithmetic?(Expression, Identifier)

Given the expression of the general term and the variable, returns a list. If the progression given by the expression is not arithmetic, the list just contains an element: `false`. Else, the list has two elements: `true` and the value , following the notation above.