The DUP method of VPGL Language duplicates (makes a copy of) the input.
DUP takes 1 input and 1 output. Input 0 must be a array or dictionary. DUP starts on arriving an array/dictionary on input 0, makes a copy of input 0, then emit 1 to output 0.
DUP makes a “shallow copy” of input 0. Shallow copy means that DUP makes a new array object which has same members of original has. DUP does not make copies of its members, so these two arrays/dictionaries share their member objects.