I have been able to find several counterexample books in some math areas. For example:
\bullet Counterexamples in Analysis, Bernard R. Gelbaum, John M. H. Olmsted
\bullet Counterexamples in Topology, Lynn Arthur Steen, J. Arthur Seebach Jr.
\bullet Counterexamples in Probability and Statistics, Joseph P. Romano, A.F. Siegel
\bullet Counterexamples in Probability and Real Analysis, Gary L. Wise and Eric B. Hall
\bullet Counterexamples in Probability, Jordan M. Stoyanov
Why are there no other examples of books in other math topics (number theory, numerical analysis, DEQs, PDEs, Dynamical Systems, Discrete Math…)?
Is it that it is just not a rich enough area, examples are too trivial, the book wouldn’t warrant publishing (low sales), someone just hasn’t written one, I missed it or something else?
Regards
Answer
The following list of titles, all of which can be found on Amazon, may help to answer the question:

Counterexamples in Optimal Control Theory

Lectures on Counterexamples in Several Complex Variables

Counterexamples in Topological Vector Spaces

Theorems and Counterexamples in Mathematics

Counterexamples in Calculus

Convex Functions: Constructions, Characterizations and
Counterexamples 
Surprises and Counterexamples in Real Function Theory

Examples and Counterexamples in Graph Theory

CounterExamples In Differential Equations And Related Topics
Attribution
Source : Link , Question Author : Amzoti , Answer Author : Michael Greinecker