I am creating questions for composition of relations, where students are expected to enter a list of ordered pairs as answers. I noticed that the answer check for multiple ordered pairs would work, but it fails when there is only one pair in the answer. Below is an example, the answer of (a,b) for the first question is marked wrong, but the answer of (a,b), (c,d) for the second question is marked correct. I also attached a screenshot of the answer checker. Is there a way to fix this problem? Thanks.

Context("Numeric");

foreach my $i(a..z) {

Context()->strings->add($i=>{});

}

$a1 = Compute("(a,b)");

$a2 = Compute("(a,b), (c,d)");

BEGIN_PGML

Enter [`(a, b)`] [____________]

Enter [`(a, b), (c, d)`] [____________]

END_PGML

# Answer evaluation

$showPartialCorrectAnswers = 1;

ANS($a1->cmp(entry_type=>"pair"));

ANS($a2->cmp(entry_type=>"pair"));