Developer for System z Enterprise COBOL for z/OS, Version 4.1, Compiler and Runtime Migration Guide
Applications with COBOL programs compiled with RES
If you call ILBOSTP0 to establish a reusable environment (that is, you
establish an assembler language program as the main program by link-editing
it with, and calling, ILBOSTP0), you must link-edit the assembler program
with Language Environment.