A main program is the program unit that receives control from the system when the executable program is invoked at run time.
>>-+-------------------+--------------------------------------->< '-PROGRAM_statement-'
>>-+--------------------+-------------------------------------->< '-specification_part-'
>>-+----------------+------------------------------------------>< '-execution_part-'
>>-+--------------------------+-------------------------------->< '-internal_subprogram_part-'
>>-END_PROGRAM_statement---------------------------------------><
A main program cannot contain an ENTRY statement, nor can it specify an automatic object.
A RETURN statement can appear in a main program. The execution of a RETURN statement has the same effect as the execution of an END statement.