TY - JOUR AU - J. Paris AU - G. Mills TI - Closure properties of countable non-standard integers JO - Fundamenta Mathematicae PY - 1979 SP - 205 EP - 215 VL - 103 IS - 3 PB - mathdoc UR - http://geodesic.mathdoc.fr/articles/10.4064/fm-103-3-205-215/ DO - 10.4064/fm-103-3-205-215 LA - en ID - 10_4064_fm_103_3_205_215 ER -