turning back now to the embodiment shown in fig2 each of the first portion side walls 32 includes a first score line 60 a second score line 62 a coextensive with the longitudinal side edges 26 s and a third score line 62 b the first second and third score lines 60 62 a and 62 b are preferably perforated in order to allow the blank 20 to be manually broken or torn therealong and facilitating the removal of the removable third side wall segment 78 it will be understood that various modifications of this arrangement may be made resulting in the removable third side wall segment having a variety of different shapes however if a preferred embodiment the removable third side wall segment will not in any event be substantially triangular in shape in other embodiments the non removable segment s of each side wall do not comprise two substantially triangular side wall segments of substantially identical size see fig7 a 7 b 7 c in addition very preferably at least one of the first score line 60 and the second score line 62 a adjoins the transverse score line 50 more preferably both of the first score line 60 and the second score line 62 a adjoin the transverse score line 50 and intersect the transverse score line 50 at points 66 generally located at corresponding longitudinal side edges 26 s of the first portion 26 although each of the side walls 32 may include a side wall first segment 74 and a side wall second segment in the embodiment pictured in fig2 there.