两个圆倒圆

lsmb

entity/pt1,obj1,obj2,pt2,pt3,obj

pt1 =point/0,0,0
pt2 =point/8,0,0
pt3 =point/15,12,0
obj1 =circle/center,pt1,radius,12
obj1 =circle/center,pt2,radius,12

obj=fillet/ln1,ln2,center,pt3,radius,3,notrim
halt

我刚接触grip，想实现圆obj1和圆obj2倒圆，我这样写为什么不对啊obj=fillet/ln1,ln2,center,pt3,radius,3,notrim出错，实现两个圆倒圆，请各位指教，谢谢！两条直线可以这样写，圆不可以吗？