Favoring shorter solutions at the expense of some loss in performance is known as parsimony, and it has already been successfully used in genetic programming (Koza, 1992).
the final formula for the fitness function we used incorporates the parsimony factor and is given by where F 1 (j) is the F 1 score (ranging from 0 to 1) of the solution j, η is the parsimony factor, L max is the maximal size (measured in number of nodes), and L(j) is the size of solution j.