Some classical zen gardens, like Daisen-in, have symbolism that can be easily read; it is a metaphorical journey on the river of life. Others, like Ryōan-ji, resist easy interpretation. Many different theories have been put forward about what the garden is supposed to represent, from islands in a stream to swimming baby tigers to the peaks of mountains rising above the clouds 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."