[QUESTION] Understanding how OpenCASCADE works

I am currently reading these books:

https://www.amazon.com/Solid-Modelling-CAD-Systems-Survive/dp/0857292587

and:

https://www.amazon.com/Boundary-Representation-Modelling-Techniques-Stro...

And i'm researching on how CAD software like OpenCASCADE works, i'm in the part of how extrusion algorithm works but i don't understand the algorithm given by the book. 

I would like to know how to sutdy the source code or how to search the functions implied in the operations like extrusion (but the source code is some complicated), i had read some about euler operators but i don't know if that is really used by OpenCASCADE.

Thank you and sorry for the english

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