For students, there is also a union operation (indicated by a capital "U"), so a student could write "(-infinity,-2) U (2,infinity)" as an answer. There is no built-in method for students to write intersections (though it certainly would be possible to write an extension that does that).

For use within the code of a problem, you can use

$ans5 = Compute("(-inf,-2) U (2,inf)");just like a student can. If you have two intervals (or sets or unions), then you can use simple addition to get unions:

$B = Compute("(-infinity,-2)"); $C = Compute("(2,infinity)"); $D = $B + $C; # equivalent to Compute("$B U $C");Similarly, you can use subtraction for set difference:

$D = Interval("(-10,10)") - Set(-1,0,1);You can obtain set intersections via methods of the interval, set, and union objects:

$B = Compute("(0,2pi)"); $C = Compute("(-pi,pi)"); $D = $B->intersect($C); # equivalent to Compute("(0,pi)");There are other methods like

`isSubsetOf`

, `contains`

, `isEmpty`

, `intersects`

, `reduce`

and `isReduced`

that can be used on interval, set, and union objects as well. The first of these returns true or false depending on whether the condition is true; `reduce`

takes a union and rewrites it without redundancy (e.g., overlapping intervals are simplified); the last returns true/false depending on whether it is already in that form.
Hope that answers your question.

Davide