Problem Statement

Inheritance is an operation of type algebra that creates a new type from one or several parent types. The obtained type is called derived type. It inherits some of the properties of its parent types. Usually inherited properties are:

The class of the new type is a   subclass   of the classes rooted in the parent types. When all (in certain sense) properties of the parents are preserved by the derived type,   it is said to be a Liskov subtype. When properties are preserved then the derived type is substitutable for its parents in all contexts.   Usually full substitutability is achievable only in some contexts.

Inheritance is

Some single inheritance languages usually allow multiple inheritance for certain abstract types, interfaces in particular. Inheritance can be considered as a relation parent-child. Parent types are sometimes called supertype, the derived ones are subtype.   This relation is transitive and reflexive. Types bound by the relation form a wp:Directed_acyclic_graph directed acyclic graph (ignoring reflexivity). With single inheritance it becomes a tree.

Show a tree of types which inherit from each other.

The tree should look like this:

Let's start with the solution:

class Animal ()
end
 
class Dog : Animal  ()
end
 
class Cat : Animal  ()
end
 
class Lab : Dog  ()
end
 
class Collie : Dog ()
end