#2 let properties defined on sets

[Jörn Guy Süß]

let properties should behave like regular properties.

In the expression below,

allParents is undefined on self.parent, because
self.parent is a set.

def:

let parent : Set(GeneralizableElement) =
self.generalization.parent->asSet()

def:

let allParents: Set(GeneralizableElement) = self.parent-
>union(self.parent.allParents)