Little combination problem

[jbv]

Hi list,

I'm facing a little combination problem in which I'm getting lost...

I have a string tof n letters (n can range from 2 to 20)
and I need to produce all possible combinations of n-1 to 2 letters.

for example :
    string : ABCD

    combinations to output :
    ABC
    ABD
    ACD
    BCD
    AB
    AC
    AD
    BC
    BD
    CD

I'm trying to do it with nested loops but don't get anywhere...

Any idea ?

Thanks,
JB