Problem with "is"



Hi,

I got the following in Maxima:

(%i1)  declare(a,real,b,real);
(%o1)                                done
(%i2) c:a+b;
(%o2)                                b + a
(%i3) is(c^2>0);
(%o3)                               unknown

I know that "is" in Maxima is not very strong, but this is really
trivial. Is there something I'm doing wrong? Thanks,

Best Regards

Sergio