In the prehistory of formal language theory: Gauss languages [chapter]

Lila kari, Solomon Marcus, Gheorghe Paun, Arto Salomaa
1993 Current Trends in Theoretical Computer Science  
The problem proposed by Gauss of characterizing the code of a simple crossing closed curve (SCCC, for short) can be considered a formal language question. We define three related infinite languages. Two of them are regular; the type of the third is an open problem.
doi:10.1142/9789812794499_0041 dblp:series/wsscs/KariMPS93 fatcat:hpu3weoac5dhjms3iso45a46iu