** Using WeBWorK **

In the following, an interval [5.099, 5.101] is defined. The endpoints are so close, that default tolerances make WW treat them as equal. So I understand why the interval ends up printing as a single value, [5.099].

However nothing seems to be acceptable to enter this into the answer blank. Entering [5.099] gives the message:
Your answer isn't an interval, set or union
(it looks like a real number)

And entering [5.099, 5.101] gives the message:
The parentheses for your set are of the wrong type

What's going on here?

For now I will advise the author to tighten the tolerance, and I think all will be well. But I wanted to post in case this identifies a bug.

DOCUMENT();

loadMacros(
 "PGstandard.pl",
 "MathObjects.pl",
 "PGML.pl",
);

##############################################
TEXT(beginproblem());

$a = 5.1;
$b = 0.001;

Context("Interval");
$c = $a-$b;
$d = $a+$b;
$ans = Compute("[$c,$d]");

##############################################
BEGIN_PGML
Enter [`[$ans]`].

[_______________]{$ans}

END_PGML
##############################################

ENDDOCUMENT();