Arvind Jan-Willem Maessen Rishiyur S. Nikhil Joseph E. Stoy A Lambda Calculus with Letrecs and Barriers. 19-36 1996 conf/fsttcs/1996 FSTTCS db/conf/fsttcs/fsttcs96.html#ArvindMNS96 http://dx.doi.org/10.1007/3-540-62034-6_34