Like any work of art, the artistic garden of Ryōan-ji is also open to interpretation, or scientific research into possible meanings. Many different theories have been put forward inside and outside Japan about what the garden is supposed to represent, from islands in a stream, to swimming baby tigers to the peaks of mountains rising above to theories about secrets of geometry or of the rules of equilibrium of odd numbers. Garden historian Gunter Nitschke wrote: "The garden at Ryōan-ji does not symbolize anything, or more precisely, to avoid any misunderstanding, the garden of Ryōan-ji does not symbolize, nor does it have the value of reproducing a natural beauty that one can find in the real or mythical world. I consider it to be an abstract composition of "natural" objects in space, a composition whose function is to incite meditation.".[13]