Morland, Leslie (1980) The steady motion of ice sheets. Journal of Glaciology, 25. pp. 229-246. ISSN 0022-1430
Siemons, Johannes (1980) Normal subgroups of triply transitive permutation groups of degree divisible by 3. Mathematische Zeitschrift, 174 (2). pp. 95-103. ISSN 0025-5874