Abstract This paper presents a complete proof of the unresolved Toeplitz Conjecture (Inscribed Square Problem) for the most general class: C⁰ Jordan closed curves. The proof is based on the existence theorem for C¹ curves using the Brouwer Degree and its extension to the C⁰ class via the Stability Theorem of Degree. The core argument revolves around guaranteeing the permanence of the zero set. This concept is formally defined as the existence of a zero set Z (F) situated at a distance > 0 from the boundary T⁴ of the parameter space. This condition rigorously avoids the degeneration of the inscribed square during the limiting process, thereby affirmatively resolving the C⁰ Toeplitz Conjecture.
Ueoka, Yoshiki (Thu,) studied this question.