The 70 corners of the 14 polygons consist of 35 corners (denoted by black yods) associated with one set of seven polygons and 35 corners (denoted by red yods) associated with the other set. Constructed from tetractyses, the outer Tree of Life, likewise, is made up of 70 yods, 35 of which (red yods) belong to its trunk, the remaining 35 black yods belonging to its branches. This differentiation and its counterpart in the inner form of the Tree of life has a profound, fundamental significance. Loosely speaking, it signifies the metaphysical distinction between 'physical' and 'superphysical' aspects of any holistic system designed according to the universal blueprint of the Tree of Life (a human being, for example). In superstring theory, where the holistic system in question is what is known as the 'E₈×E₈' heterotic superstring,' the two mirror-image halves of the inner Tree of Life appear as the distinction the theory makes between ordinary matter and so-called 'shadow matter'. This is because, as will be seen in the Superstrings as sacred geometry section, one half encodes the physics of superstrings making up ordinary matter, whilst the other half encodes the physics of shadow matter superstrings, their mirror symmetry explaining why the unified force of each type of superstring is described by the same symmetry group E₈.