Some problems have more than one correct answer, each of type "function". E.g., "Find a function* f*, with *f*(0) nonzero, satisfying the identity *f*"(*x*)+*f*(*x*)=0 for all *x*." What is the approved method for checking student submissions in such questions?

For the example here, my first idea is to build a custom answer-checker that assigns the student's response to an object $f, and then defines

my $z = $f->D('x','x') + $f;

Now I just need to determine if $z coincides with the zero function. I know that the answer-checker built in to WW does this kind of thing all the time. Is there a standard way for me to access this functionality in the current situation? (Right now I evaluate $z for a bunch of x-values and add up the moduli of the values I get, hoping for a very small sum. This feels like reinventing the wheel.)

This example is a simple representative for a whole class of problems, so I'm hoping to arrive at a rather general solution eventually. Nonetheless, a suggestion customized to this particular instance would already expand my understanding and be much appreciated.