Up until the 1970s, Hal Busse recurrently returned to a strictly geometrical vocabulary—which, however, was fundamentally different from the Concrete art that became increasingly prevalent in the late 1960s. The sculpture Alleen [Avenues] created in 1967 is a good example of this. It consists of Plexiglas squares and square aluminum pipes, all in the same format, colored red, blue, and yellow. Based on a selection of three sizes, three bodies composed of spheres in various combinations are mounted within each of these pipes. Viewers are invited to imaginatively transfer the open squares, thus composing new constellations. The series of artworks to which this sculpture belongs was thus subsequently renamed Wandelbare Türme [Alterable Towers] by Busse. Hal Busse created an extensive and diverse oeuvre without coming to public attention. In 1957, Busse began to produce constructivist work—her status as a pioneer in Germany in this context has hitherto been overlooked.