Only "Some" books have a solution, and not in all editions, our priority is to publish the Solution along with the Book in its respective edition so that the problems of the book are consistent with the exercises solved in the solution.
If you only find the book in one publication, it is because we do not have the solution for that Edition; or maybe there is no such, but you should also look in another edition. To do this, just click on the name of the author of the book and you will be able to view all the editions that we have of it.
In certain books, mainly science, physics and chemistry; the solution of one edition can be used for others, since many of the problems that it brings are the same between one edition of the book and another, or they are simply in a different order.
Note that only the most recent editions have Solvers.