subscripted variables for display



I  would like to be able to compute the eigenvalues of the 
matrix

A : matrix([-lambda[1],lambda[1]],[mu[1],-mu[1]])

using eigenvalues().  Maxima reports an error:

Maxima encountered a Lisp error:

  Type-error in KERNEL::OBJECT-NOT-LIST-ERROR-HANDLER:  1 is 
not of type LIST

Now I am using the array lambda purely for aesthetic (nice 
display) purposes, in the TeXmacs front end.  That is, I 
don't care about the fact that lambda[2] comes after 
lambda[1], etc.  And I have another matrix

B : matrix([-lambda[2],lambda[2]],[mu[2],-mu[2]])

that uses related notation.   Is there some way to make 
maxima treat lambda and mu purely as symbols?
Or is there some other way to achieve subscripting?

						Kostas