Completeness for the Complexity Class

Exhibiting a deep connection between purely geometric problems and real algebra, the complexity class ∃R plays a crucial role in the study of geometric problems. Sometimes ∃R is referred to as the 'real analog' of NP. While NP is a class of computational problems that deals with existentially quantified boolean variables, ∃R deals with existentially quantified real variables. In analogy to Π2p and Σ2p in the famous polynomial hierarchy, we study the complexity classes ∀∃R and ∃∀R with real variables. Our main interest is the Area Universality problem, where we are given a plane graph G, and ask if for each assignment of areas to the inner faces of G, there exists a straight-line drawing of G realizing the assigned areas. We conjecture that Area Universality is ∀∃R-complete and support this conjecture by proving ∃R- and ∀∃R-completeness of two variants of Area Universality. To this end, we introduce tools to prove ∀∃R-hardness and membership. Finally, we present geometric problems as candidates for ∀∃R-complete problems. These problems have connections to the concepts of imprecision, robustness, and extendability.