Terme, Positionen

>> prog::exprtree((2*k+1)!!)
                       fact2
                       |
                       `-- _plus
                           |
                           +-- _mult
                           |   |
                           |   +-- k
                           |   |
                           |   `-- 2
                           |
                           `-- 1
>> op((2*k+1)!!,[1,1,2])           2