Complex sentence: There are two improper regular tilings:, an apeirogonal dihedron, made from two apeirogons, each filling half the plane; and secondly, its dual,, an apeirogonal hosohedron, seen as an infinite set of parallel lines.
Split into simpler sentences: There are two improper regular tiling,, an apeirogonal dihedron, made from two apeirogons, each filling half the plane. And secondly, its dual,, an apeirogonal hosohedron, seen as an infinite set of parallel lines.