Hello, A bug in STABLE-SORT on empty vectors. CL-USER(1): (lisp-implementation-version) "1.5.0-dev-svn-14939" "OpenJDK_64-Bit_Server_VM-Oracle_Corporation-1.7.0_111-b01" "amd64-Linux-3.2.0-4-amd64" CL-USER(2): (stable-sort #() '<) #<THREAD "interpreter" {7454F875}>: Debugger invoked on condition of type TYPE-ERROR Invalid array index 0 for #() -- Eric Marsden https://risk-engineering.org/