Hacker News Reader

So if I were to write a book named A Game of Thrones, under the pen name George R. R. Martin, would it be permissible by law to publish it?

As far as copyright law is concerned, yes.

However, you would be in violation of trademark law.

API is more like the table of content of a book, not titles. Titles would be like the website name.

They can, however, be trademarked.

Sure, but only once the title has attained secondary meaning over and above the words in the title. Basically, it has to be beyond the level of a bestseller. Most book titles don't come anywhere close.