ancestor(x,y)
The ancestors of y are y, parent y, parent parent y, and so on.
If x is an ancestor of y, then we also say that y is a specialization of x.
i1 : parent String o1 = Net o1 : Type
i2 : parent parent String o2 = Thing o2 : Type
i3 : parent parent parent String o3 = Thing o3 : Type