From: JinKyu on
If we want to use one symbolic expression co1, which is co1=a*x+b*y+c*z, in the complex expression such as U=-2*(a*x+b*y+c*z) + etc...., what should we do?
(Here, a,x,b,y,c,z, etc are all symbolic variables.)

There, I want to have the abbreviate expression for U as U=-2*co1 + etc...

Thanks