The distinction between strong [Liskov-Wing93b] [Liskov-Wing94]
and weak [Dhara-Leavens94b] behavioral subtyping
only affects the inheritance of history constraints.
Recall that a weak behavioral subtype is specified by using weakly
in a simulates-clause that names the supertype.
If this is not done, then strong behavioral subtyping is assumed.
For a strong behavioral subtype, all of the subtype's member functions
must satisfy the supertype's history constraint;
that is, unless weakly is used, the history constraints are inherited
unchanged by the subtype and apply to all member functions in the subtype,
even new ones.
Because of this,
instances of the subtype can be manipulated through aliases
using the interface of both its supertype and its own type
[Liskov-Wing93b] [Liskov-Wing94].
In a weak behavioral subtype, the history constraint is only applied to the member functions inherited from the supertype. See section 7.9.2 Inheritance with Explicitly-Given Traits and Weak Subtyping above for an example.
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