### 2.34.2 Boundaries of an interval : `left right`

`left` (resp `right`) takes as argument an interval.
`left` (resp `right`) returns the left (resp right) boundary of this interval.
Note that `..` is an infixed operator, therefore:

- `sommet(1..5)` is equal to `’..’` and `feuille(1..5)` is equal to `(1,5)`.
- the name of the interval followed by `[0]` returns the operator `..`
- the name of the interval followed by `[1]` (or the `left` command) returns the left boundary.
- The name of the interval followed by `[2]` (or the `right` command) returns the right boundary.

Input :

`(3..5)[0]`

Or :

`sommet(3..5)`

Output :

`’..’`

Input :

`left(3..5)`

Or :

`(3..5)[1]`

Or :

`feuille(3..5)[0]`

Or :

`op(3..5)[0]`

Output :

`3`

Input :

`right(3..5)`

Or :

`(2..5)[2]`

Or :

`feuille(3..5)[1]`

Or :

`op(3..5)[1]`

Output :

`5`

Remark
`left` (resp `right`) returns also the left (resp right) member of an equation (for example `left(2*x+1=x+2)` returns `2*x+1`).