pretty printing

[durrieu@tantale.cert.fr (Guy Durrieu)]

Hello,

I would like to pretty print expressions with imbricated if statements in the
following way:

C = if C1 then if C2 then A
               else B
    else if C3 then if C4 then A+B
                    else A-B
    else if C5 then A*B
    else if C6 then A/B
    else B;

(The "else" branches of the imbricated if statements would be pretty printed at
the same level).

I guess this result could be obtained using things such !prlevel... but I 
didn't succeed.

Any help would be appreciated.

-- Guy DURRIEU.