I want to define a non-terminal node in GP that can have different number of children. For example, in a case it has two children, and in another case 5 children. However, it must have at least one child. I tried to define a constrain with no size, but it does not work. #No size is set gp.nc.1 = ec.gp.GPNodeConstraints gp.nc.1.name = undefinedChildren gp.nc.1.returns = nil Please let me know how can I define a node capable of having different number of children. Thanks. Tomas.