Question

Question #2136e

Answer 1

Closed interval: specified end points are included.
Open interval: specified end points are not included.
Half-open = half-closed interval: one of the specified end point is included but not the other.

Explanation:

An interval is identified by specifying the end point values of the interval.

It may be written (for example) as something like:
`color(white)("XXX") x in [4,7]`
This is an example of a closed interval which indicates that `x` could be `4`, or any value between `4` and `7`, or `7`.

As an alternative we might have:
`color(white)("XXX")x in (4,7)`
which is an open interval which indicates that `x` could be any value between `4` and `7` but not `4` or `7`.

A half-open interval might look like
`color(white)("XXX")x in (4,7]`
...any value greater than but not equal to `4` up to and including `7`
or
`color(white)("XXX")x in [4,7)`
...which would include `4` but exclude `7`