Beckmann, A., & Arnold, B. (2002). A non-well-founded primitive recursive tree provably well-founded for co-r.e. sets. Archive for Mathematical Logic, 41(3), pp. 251-257. doi:10.1007/s001530100107

Beckmann, Arnold, and Beckmann Arnold. "A Non-well-founded Primitive Recursive Tree Provably Well-founded for Co-r.e. Sets." Archive for Mathematical Logic 41, no. 3 (2002): 251-257.

Beckmann, Arnold, and Beckmann Arnold. "A Non-well-founded Primitive Recursive Tree Provably Well-founded for Co-r.e. Sets." Archive for Mathematical Logic 41.3 (2002): 251-257.