"Invariant" is an exciting fantasy novel written by the famous Ukrainian writer Oleksandr Biletsky. In this book, readers will find themselves in a unique world where reality is intertwined with fantasy, and science with magic. The main character, an expert physicist, accidentally discovers a way to travel in time and space, which leads him to incredible adventures and discoveries. He finds himself in other dimensions, with strange creatures, and faces the dangers of his discovery. The author skillfully combines scientific facts and fantastic elements, creating a unique world that fascinates and leaves questions about the essence of invariance. "Invariant" is a book that will grab you and won't let you go until the last page.