Atoms of an expression

How is it possible to get GiNaC to yield all the atoms occuring in an expression? (i.e. return a list of all the leaves of the expression tree). This is of interest in the generation of sparse jacobian / hessian matrices as one example of applications. Vassilis ----------------------------------------------------------------- Dr. Vassilis S. Vassiliadis, Lecturer, UNIVERSITY OF CAMBRIDGE, DEPARTMENT OF CHEMICAL ENGINEERING Pembroke Street, Cambridge CB2 3RA, UK. e-mail: vsv20@cheng.cam.ac.uk -----------------------------------------------------------------