Useful Polymorphism in C

Hereby I publish a draft of a paper, Useful Polymorphism in C, where you could find some interesting and straightforward features of Object Oriented languages applied to our favourite language. It relies in the C structures to simulate the OO polymorphism and in organizing the headers and source files in a way in helps to achive the goal.
I am not sure if I will finish the paper ever but it has enough literature to understand the whole idea and contains quite lines of code which helps to go ahead and get it working.
I know a bunch of stuff have been written about OOing C but here I just try to apply the semantic of Polymorphism avoiding the use of hilarious syntax. I hope find it interesting.