The following creates an object with two slots: 

```
 translate([-40,-40,0]) difference() {
     cube ([90,28,12]);
     translate([12,-.01,5]) cube([12.7,28.02,14.02]);
     translate([65,-.01,5]) cube([12.7,28.02,14.02]);
```

How can the first main cube be extended to be a complex object of the syntax:

    cube([60,20,10],center=true);translate([0,0,5])cube([30,20,10],center=true);

and then use `difference` to create holes?