A torus, cut in a certain way, may produce strange things. I shall illustrate this in the third seminar, shifting the historical context into the twentieth century. A number of important artistic practices which have been developed since the 1930s are in some way or another connected to topology, the modem mathematical discipline formerly known as Analysis Situs. References to, borrowings from and, in some rare cases, even critiques of topology (or what one imagined to be topology) are to be found, for instance, in concrete art since ca. 1935 (cf. the once hugely influential work of Max Bill) as well as in several post-WW II practices critically related to concrete art (Lygia Clark and Brazilian neoconcretismo, Dieter Roth, etc.); in the historically most significant (neo-)avant-garde movement of the time around 1960, i.e., Situationism (some writings of Asger Jorn, etc.); in different kinds of video art or, more generally, post-minimal art of the 1960s and 70s (Dan Graham ... ); in the so-called topological trend in architecture since the 1990s (for instance, the architecture and writings of Peter Eisenman). In many of the different historical settings indicated by these names, one thing keeps re-appearing, namely: the Moebius band. Artists and architects didn't only design construct and/or manipulate sculptures, buildings, video installations et cetera which can literally or metaphorically be described as Moebius bands. They would also – and in some cases, exclusively – make use of the Moebius band as a conceptual model or as a weapon against certain kinds of conceptualizations.