diff --git a/books/free-programming-books-subjects.md b/books/free-programming-books-subjects.md
index ebd7ac462c400..2f13d5e7e9945 100644
--- a/books/free-programming-books-subjects.md
+++ b/books/free-programming-books-subjects.md
@@ -199,7 +199,7 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 
 
 ### Competitive Programming
-
+=======
 * [Competitive Programmer's Handbook](https://cses.fi/book/book.pdf) - Antti Laaksonen (PDF) `(CC BY-NC-SA)`
 * [Competitive Programming, 1st Edition](https://cpbook.net/#CP1details) - Steven Halim [(PDF)](https://www.comp.nus.edu.sg/~stevenha/myteaching/competitive_programming/cp1.pdf)
 * [Competitive Programming, 2nd Edition](https://cpbook.net/#CP2details) - Steven Halim [(PDF)](https://www.comp.nus.edu.sg/~stevenha/myteaching/competitive_programming/cp2.pdf)
@@ -238,7 +238,7 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 * [Computational Thinking](https://www.cs.cmu.edu/~15110-s13/Wing06-ct.pdf) - Jeannette Wing, Carnegie-Mellon University (PDF)
 * [Computer Science Class XI](https://cbseacademic.nic.in/web_material/doc/cs/1_Computer-Science-Python-Book-Class-XI.pdf) - CBSE (PDF)
 * [Computer Science Class XII](https://cbseacademic.nic.in/web_material/doc/cs/2_Computer_Science_Python_ClassXII.pdf) - CBSE (PDF)
-* [Computer Science I](https://cse.unl.edu/~cbourke/ComputerScienceOne.pdf) - Chris Bourke (PDF) (CC BY-SA) 
+* [Computer Science I](https://cse.unl.edu/~cbourke/ComputerScienceOne.pdf) - Chris Bourke (PDF) (CC BY-SA)
 * [Computer Science II](https://cse.unl.edu/~cbourke/ComputerScienceTwo.pdf) - Chris Bourke (PDF) (CC BY-SA)
 * [CS Principles: Big Ideas in Programming](https://www.openbookproject.net/books/StudentCSP/) - Mark Guzdial, Barbara Ericson (HTML)
 * [Pull Requests and Code Review](https://scs.tl/book-pr) – Sebastien Castiel
@@ -705,7 +705,7 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 ### Object Oriented Programming
 
 * [Object Oriented Programming](https://www.cl.cam.ac.uk/teaching/0910/OOProg/OOP.pdf) - Robert Harle (PDF)
-* [OOP – Learn Object Oriented Thinking and Programming](https://files.bruckner.cz/be2a5b2104bf393da7092a4200903cc0/PecinovskyOOP.pdf) - Rudolf Pecinovsky (PDF) 
+* [OOP – Learn Object Oriented Thinking and Programming](https://files.bruckner.cz/be2a5b2104bf393da7092a4200903cc0/PecinovskyOOP.pdf) - Rudolf Pecinovsky (PDF)
 
 
 ### Open Source Ecosystem
@@ -901,7 +901,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [Domain Driven Design Quickly](https://www.infoq.com/minibooks/domain-driven-design-quickly)
 * [Domain-Driven Design Reference](https://www.domainlanguage.com/ddd/reference) - Eric Evans (CC BY)
 * [DSL Engineering: Designing, Implementing and Using Domain-Specific Languages](http://dslbook.org) - Markus Voelter
-* [Evidence-based Software Engineering](http://knosof.co.uk/ESEUR) - Derek M. Jones (PDF) (CC BY-SA) 
+* [Evidence-based Software Engineering](http://knosof.co.uk/ESEUR) - Derek M. Jones (PDF) (CC BY-SA)
 * [Exploring CQRS and Event Sourcing](https://docs.microsoft.com/en-us/previous-versions/msp-n-p/jj554200(v=pandp.10)) - Dominic Betts, Julián Domínguez, Grigori Melnik, Mani Subramanian, Fernando Simonazzi ([EPUB, PDF](https://www.microsoft.com/en-us/download/details.aspx?id=34774) - [code samples](https://go.microsoft.com/fwlink/p/?linkid=258571))
 * [Guide to the Software Engineering Body of Knowledge](https://www.computer.org/education/bodies-of-knowledge/software-engineering/v3) (email address *requested*)
 * [How to Design Programs](https://www.htdp.org)