symbolically replace expressions in maxima

Question

I'm having trouble finding out how to do this:

x=a+b
y=c+d
z=x*y

I would like the output to be

z=ac+ad+bc+bd

not

z=xy

Answer 1

Like this?

(%i1) x: a+b;
(%o1)                                b + a
(%i2) y: c+d;
(%o2)                                d + c
(%i3) z: x*y;
(%o3)                           (b + a) (d + c)
(%i4) z: expand (z);
(%o4)                        b d + a d + b c + a c
(%i5) 

Assignment in maxima is done by :, not = (which is used for checking for equality)