First night
Second night
Third night
Fourth night
Fifth night
Sixth night
Seventh night
Eighth night
The ninth night
The tenth night
The Eleventh Night
Twelfth Night

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Acknowledgements
Translator's Note

The wonderful principles of mathematics unfolding in the dream world
Robert meets the Math Demon for twelve nights and experiences strange mathematical phenomena.
In fact, Robert hates math, and he doesn't like his math teacher, Dr. Bokel.
But the Math Genius appears in Robert's dreams and magically teaches him fun math.
The terminology used by the Math Genius is not typical mathematical terminology, but rather something special.
'Jump up' is exponentiation, 'pull up roots' is finding square roots, 'approximate numbers' is prime numbers, and 'bang' is factorial. These expressions are different from those used in school, adding fun and helping students remember the characteristics of the concepts.
The concepts Robert learns over the twelve nights are:


First night? Number 1, infinitely large number, infinitely small number
Second Night? Number 0, Roman numerals, decimals, negative numbers, jumping (exponentiation)
Third night? Division, approximate numbers (decimals)
Fourth night? Prime numbers, recurring decimals, irrational numbers, roots (square roots)
Fifth night? Triangular numbers, square numbers
Sixth Night? Fibonacci Sequence
Seventh Night? Number Triangle (Pascal's Triangle) Eighth Night? Permutations, Combinations, Bang (Factorial)
The ninth night? Ordinary numbers (natural numbers), infinity, series
Tenth Night? Irrational Numbers, the Golden Ratio, Euler's Rule: Theorems of Polyhedra
Eleventh Night? Proof, Proposition, Axiom
Twelfth Night? Klein Bottle, Imaginary Numbers (i), Pi (π), Math Fools

It covers a wide range of important topics in mathematics, from basic concepts like natural numbers, real numbers, and irrational numbers to high school-level infinite series and Euler's law, which is the basis of topology.
Meanwhile, on the twelfth night, Robert, who was invited to the Math Hell or Math Heaven, follows the Math Demon Teplotaxl and meets famous Math Demons, that is, historical mathematicians, such as Russell, Klein, Cantor, Euler, Gauss, Fibonacci, Pythagoras, Pascal, and Cantor.
Robert is surprised that there are so many Math Geniuses and only six or seven women, and the Math Genius explains that he used to think math was a man's job, but that will change.
And Robert receives a precious gift from another math genius.


A math book that conveys surprising mathematical phenomena in an interesting way.
One of the most common mistakes made when teaching mathematics is giving too much detail in advance.
Like other natural principles, learning mathematics requires time to savor surprising phenomena, to wonder, and to reflect on them.
However, explaining math too much to children often has the unfortunate result of stifling their growing curiosity.
This book succeeds in extracting the secrets and principles of mathematics through surprisingly simple conversations.
This book is special in that it refrained from direct explanation and conveyed the reader to the novel pleasure of the phenomenon itself.
However, it does not simply present the basic principles of mathematics, but cleverly combines mathematical content with literary devices.

Because mathematical phenomena unfold in the imaginary world of dreams, it has a special charm that allows for freer thinking.
There's a piece of gum shared with people all over the world, a giant iron pillar shaped like the number 1, a snake with the number 9 biting its own tail, flying number mosquitoes, a giant fluffy flour counter, and numbers filling Robert's bedroom.
Because it is a dream, the unrealistic descriptions stimulate curiosity and allow us to feel the mystery of mathematics.

Additionally, the background of each chapter is closely related to the mathematical content covered therein.
For example, by setting the dream setting as a 'cave with no exit' to suggest that there is no general rule for determining prime numbers, that is, that there is no magic trick for determining prime numbers, the literary device is used to express mathematical phenomena and make them more comprehensively understandable.
And by changing mathematical terms into interesting words, it stimulates the reader's interest.
For example, exponentiation is written as jumping, square root as uprooting, and combination as changing places, making it easy to understand the concepts naturally.
Meanwhile, the story's fun begins with Robert and the math genius engaging in a strange war of nerves, but gradually growing fond of each other.
On the last night, Robert is recognized as a student learning the magic of numbers, and he easily solves Dr. Bokel's problems. The amazing transformation that has taken place in a child who hated math is quite touching.
All these elements work together to naturally transport the reader into a world of mathematics, guided by a math genius, a world where questions are endless, imagination reaches infinity, and surprising secrets abound.