• The strength of countable saturation 

      van den Berg, Benno; Briseid, Eyvind Martol; Safarik, Pavol (Journal article; Peer reviewed, 2017)
      In earlier work we introduced two systems for nonstandard analysis, one based on classical and one based on intuitionistic logic; these systems were conservative extensions of first-order Peano and Heyting arithmetic, ...