Peter Zahn. A Predicative Approach to Nonstandard Mathematics. Math. Log. Q., 33(1):85-96, 1987. [doi]
@article{Zahn87-0, title = {A Predicative Approach to Nonstandard Mathematics}, author = {Peter Zahn}, year = {1987}, doi = {10.1002/malq.19870330111}, url = {http://dx.doi.org/10.1002/malq.19870330111}, researchr = {https://researchr.org/publication/Zahn87-0}, cites = {0}, citedby = {0}, journal = {Math. Log. Q.}, volume = {33}, number = {1}, pages = {85-96}, }