The Book of French Mathematician Jacques Hadamard
The Psychology of Invention in the Mathematical Field.
https://www.amazon.fr/Psychology-Invention-Mathematical-Field/dp/0486201074
The book discusses the four stages of thought :
1); Preparation (conscious work setting up the problem and trying to solve it)
2); incubation (no conscious work on the problem)
3); illumination (the fruits of incubation where an insight is received) and finally
4): verification (consciously testing and verifying the insight)
Gromov's Ergobrain Program for Universal learning program
Great Circle of Mysteries Mathematics, the World, the Mind Authors: Gromov, M.