It is consistent that there exists an ordered real closed field which is not hyper-real. Stojanović, Jadran; Perović, Žikica — 1997 Publications de l'Institut Mathématique. Nouvelle Série
About An Equivalent Of The Continuum Hypothesis Žikica Perović — 1982 Publications de l'Institut Mathématique
A Remark on Subsets of Free Boolean Algebras Žikica Perović — 1988 Publications de l'Institut Mathématique
Pseudo-galois Extensions of Boolean Algebras Žikica Perović — 1993 Publications de l'Institut Mathématique