Group is
# if defined(X_Y)
#    error X_Y defined !
# endif
	a.sml
# if not defined (structure A)
#    error No definition for structure A!
# endif
	b.sml : sml
	c.sml
# if (3 > 2)
	3.sml
# elif not (4 > 5)
        4.sml
# else
        5.sml
# endif
