Mathematical Labyrinths.
It goes over the key steps in approaching a difficult problem, contemplating a plan for its solution, and discusses set of mental models to solve math problems.
The book is not a routine set of problems..
The essential idea is a framework laid upon the reader on how to solve nonconventional problems -- particularly in the realm of mathematics and logic.
Pathfinding provides an overview of various non-standard problems and the approaches to their solutions.
Mathematical Labyrinths