Why is an empty list returned when solving for thi

Question

I'm trying to solve a simple linear system in Maxima using solve like so:

/*Standard form*/
eq1 : x1 + 3*x2  + s1 = 6;
eq2 : 3*x1 + 2*x2 + s2 = 6;

base1 : solve([eq1,eq2],[s1,s2]);

This however returns an empty list and I don't know why. Any ideas? I'm pretty sure the system has a solution, so that shouldn't be the issue.

EDIT:

I attempted to insert the equations explicitly into solve in place of eq1 and eq2, and now it works. Now the question is, why do I need to explicitly insert the equations to be solved for into the first argument of solve. An in-depth answer about how Maxima works in this case would be welcome.