Hello, I have been reading the ECJ-Interest list for a while, and I find it really interesting... I hope that my question is not too stupid, but I really have problems using ADFs. I am trying to solve a system of n equations using an ADF implementation. I managed to represent it as the following tree : Master Tree | Result Producing Branch | | | ADF0 ADF1 ... ADFn If I generate a system containing 3 variables like : (X1 = a variable given from a learning sample) X2 = X1 + X1 X3 = X1 * X2 Where ADF0 corresponds to the equation establishing the value of X2 and contains the X1 + X1 , and ADF1 corresponds to the value of X3 ands contains X1*X2... My problem is that, as ADF0 returns the value of X2 and ADF1 returns the value of X3, I would like the result prucing branch to take these 2 inputs and return both values to the GP problem. So I have my ADF returning a different type of variable (single variable) than the one used in the GPproblem (multiple variables)... Here is what I did: Having an operator AND(ADF..,ADF..) in the function set of the result producing branch, that would concatenate the result of each ADF into a 2 dimensional array, and an operator ONLY(ADF..) that would take the result of one ADF and return it under the format of the 2 dimensional array as well... Problem : - The result producing branch gives me a very complicated tree of unecessary lenght with a lot of ONLY and AND... Is there any way to just have one operator that would take n ADF as input , and return a 2- dimensional array of correponding size? And then limit the result producing tree structure as having only one function with n Adfs. In preparation for such an operator, I have added in the koza.params file branching up to nc20 (20 variables!). REsult-Producing Tree | ADFsReceptor -> return a 2-dimensional array of floats / | \ Adf0 Adf1 .. Adfn -> every adf returns one float Is the idea flawed ? Would you have any advice about how to implement the ADFsReceptor? Thanks !