Intro_to_Solid.md

@@ -336,3 +336,6 @@ You have to create a new mother class for these two classes like the preceding e
 
 This convention says that all classes that we use depends on the interface or abstract classes.
 Like precedents example, all methods was abstracts.
+
+>The Dependency Inversion principle states that our classes should depend upon interfaces or abstract classes instead of concrete classes and functions.
+>We want our classes to be open to extension, so we have reorganized our dependencies to depend on interfaces instead of concrete classes.