参数变换后的工资模型：log(wage)=b0+b1*educ+b2*exper+b3*(exper+tenure)+u,拟合模型时R代码为：fit<-lm(log(wage)~educ+exper+l(exper+tenure))，但运行结果显示Error in l(exper + tenure) : could not find function "l"。所以想请问一下大神，这里的“l"函数在R软件的什么程辑包中？