subroutine declared_external_subroutine
    implicit none
    print *, "Called declared_external_subroutine"
end subroutine declared_external_subroutine

subroutine undeclared_external_subroutine
    implicit none
    print *, "Called undeclared_external_subroutine"
end subroutine undeclared_external_subroutine