In the “Epilogue” of the animation series “The Garden of Sinners”, the essence of this story is settled in a dialogue on one snowy day. Conflicts between intelligence originated from spirit and soul originated from flesh are discussed, as is often the case for normal people. With scents on Odin and Thor, who do not desire anything, dichotomies based on structuralism are brought out. Beyond the structuralism, objects that are leaked out from the dichotomies are the “origin”, i.e., “empty boundary” of the universe. The term “empty boundary” is very important for the set theory in mathematics. If the boundary of a set A is empty, it is equivalent to A being both open and closed set. For any topological space X, the empty set and the whole set are always open and closed sets. If these two are the only open and closed sets, X is connected. Any open and closed subsets of the whole space X can be represented as unions of connected components, and if and only if all the subsets of X are open and closed sets, X is a discrete space. The whole set of open and closed sets on the topological space forms boolean algebra if union and intersection are treated as operators. X has dimension zero if and only if all the points have neighborhood systems constituted by open and closed sets. Thus, “empty boundary” can be related to abstract relationships among topological sets, and even also computing. “Empty boundary” is sure to be one of the key clues of the universe.
