Complex sentence: The impossible cube draws upon the ambiguity present in a Necker cube illustration; an impossible cube is usually rendered as a Necker cube in which the edges are apparently solid beams.
Split into simpler sentences: The impossible cube or irrational cube is an impossible object that draws upon the ambiguity present in a Necker cube illustration. An impossible cube is usually rendered as a Necker cube in which the edges are apparently solid beams.