Complete correctly: When calling a subroutine with the clause CALL 'SUBROUT1',...
the external subroutine SUBROUT1 will be executed, bypassing any internal subroutines.
the internal subroutine SUBROUT1 will be executed; external subroutines aren't called.
the internal subroutines will be searched for SUBROUT1; only if there isn't an internal one, the external SUBROUT1 will be executed.
an error will occur; subroutine names must never be coded between quotes.