In comparison to that, in Ref. predictor variables and constants are available for selection at every node in the expression tree superseding an identity function. If those leaf-node operands are selected on a higher layer, their children nodes as well as the other subsequent lower levels are discarded. Hence, the tree is not set up necessarily to the maximum of allowed layers. By introducing an identity function in the modified version of the MINLP, as was proposed with the theoretical formulation of problem in the first recorded publication in the open literature on the topic in chemical engineering , the binaries on branch nodes for 𝑥 0,2