Anyone who is looking for insights into the problem-solving process in mathematics is well advised to start with two books that have been in print for more than seven and three decades, respectively: How to Solve It (Pólya), first published in 1945; and The Art of Problem Posing (Brown and Walter) in 1983.
Charles F. Marion, charliemath@optonline.net, retired from Lakeland High School in Shrub Oak, New York in 2002. He continues to relish the opportunities retirement has presented to explore the mathematical landscape in greater depth.