fig1 illustrates a preferred embodiment of the present invention deployed in a standard four wheeled wire frame grocery cart possessing a cart basket 4 . the shelf is maintained in a horizontal position in the cart basket interior by support means which are comprised of projections 7 extending beyond the exterior perimeter of the main body 3 of the shelf which are resting upon horizontal frame members 6 of the cart . the main body 3 of the shelf possesses an exterior perimeter which is subtended by the interior cart perimeter . in this preferred embodiment , the support means comprises at least two projections 7 extending beyond a first linear edge 1 of the main body 3 of the shelf and at least one projection 7 extending beyond a second linear edge of the main body 3 of the shelf . the main body 3 of the shelf comprises a substantially planar , rigid structure upon which goods purchased in a grocery store , or supermarket , are expected to be found for purchase . while the main body 3 illustrated in fig1 is solid , a first preferred embodiment of the principles relating to the present invention , as illustrated in fig2 is constructed of heavy gauge wire , exactly similar to the construction of standard grocery carts . strength and durability of this construction recommend its use but the principles relating to the present invention certainly do not demand this material . it is paramount that the structure possess sufficient rigidity to withstand the weight of articles found in a grocery store and protect other goods placed below the shelf from the crush of these articles . the shelf illustrated in fig2 depicts the preferred embodiment of the means of support . a pair of projections 7 is seen upon either side of the main body 3 of the shelf and the pair extending beyond a second linear edge 2 possess an arcuate portion 17 which servers an obvious function in stabilizing the shelf in deployment upon the opposed horizontal frame members 6 of the grocery cart basket 4 . curving the projections 7 also minimizes the possibility of these projections from posing the opportunity of harm or danger to material or persons . while the projections 7 depicted in fig1 lack an arcuate portion , as do the projections 7 extending beyond first linear edge 1 of the shelf illustrated in fig2 one pair of projections extending from each of the two opposed sides of the shelf are seen , as in fig2 which exemplifies the basic structure of the means of support considered most stable and convenient in fulfillment of the principles relating to the present invention . it is noted that the prevalent construction of grocery carts in the united states is currently characterized not only by four wheels and a wire frame but also by the ability to horizontally nest a number of carts , front through back , so that the floor space required for storage of a number of such carts is minimized . in order to facilitate this feature , the vertical walls 5 of such carts are substantially parallel but must necessarily possess a small inclination from back to front such that the front wall of the cart is of a smaller width than the rear . for the purpose of clarity in this document , it is hereby noted that the phrase ` substantially parallel ` as applied to either the vertical walls 5 of a grocery cart basket or to the opposed first and second linear edges 1 and 2 of the main body 3 of the shelf representing the present invention specifically encompass a small degree of inclination with respect to the longitudinal axis of each . a further feature characterizing the standard design of grocery carts currently prevalent in the united states today are side walls which are , indeed , vertical . while this is not necessary for horizontal nesting , it does maximize the space of a basket interior with regard to material , though other factors may certainly be involved . regardless of the reason for this feature , and though it is unnecessary to the present invention , vertical walls allow an additional advantage to a horizontal shelf . given truly vertical side walls , a shelf constructed in accordance with the first preferred embodiment of the principles relating to the present invention for a particular manufacture of cart may be positioned upon several vertical levels inside the basket of the cart . given vertical side walls , the distance between any two opposed horizontal frame members upon a single vertical elevation is the same , and the distance between any two opposed horizontal frame members upon different vertical elevations is greater . therefore , it is eminently practical , therefore , to place the first linear edge of a shelf made in accordance with a first preferred embodiment of the principles relating to the present invention in communication with one interior side wall of a grocery cart of a particular manufacture and ensure that the projections extending beyond the first linear edge of the main body of the shelf will find repose upon the upper surface of one horizontal frame member . then , by simply dropping the opposed side of the shelf , it is inevitable that the projections extending beyond the second linear edge of the main body of the shelf will engage the horizontal frame member along the opposed side wall of the cart which is upon the same vertical elevation as the first horizontal member engaged , and no other , if the projections are of correct length . obviously , if the projections exceed the difference between the horizontal interior width of the cart and the distance between one horizontal frame member upon one vertical elevation and another upon a different elevation , this feature is thwarted . another feature of a first preferred embodiment of the principles relating to the present invention is depicted in fig3 . the horizontal nesting character of the standard grocery cart precludes the permanent placement of a horizontal shelf . it is desirable , in any case , to have such a shelf removed from the interior of a cart basket while placing goods , particularly perishable goods such as fruits and vegetables , upon the floor of the cart basket prior deployment of the shelf in order to support heavier bulk items safely above the perishable goods . while unessential to the present invention , another recommended feature is the inclusion of a handle providing the means to hang the shelf , prior use , from a horizontal frame member , including the top edge which is not generally strictly horizontal but is substantially so , exterior to the basket substantially flush to one of the cart side walls . a handle 9 for this purpose possesses at least one arcuate portion designed to communicate with a substantially horizontal frame member and is fixedly attached to the main body 3 of the shelf . this handle may also , if designed appropriately , serve to provide a convenient location for the placement of one &# 39 ; s fingers when either placing the shelf into position in the interior of a cart basket or removal therefrom . emphasis of this feature will minimize the possibility of one catching one &# 39 ; s fingers between a linear edge of the main body of the shelf and an interior side wall of the cart basket . a separate handle may be provided for this function in keeping with the principles of the present invention . it is simply considered most economic to combine these two purposes , that of a handle for deployment and removal and that of a hook for hanging the shelf along an exterior side wall of the cart prior use , in one attachment . while the foregoing describes in detail a first preferred embodiment of principles relating to the present invention as well as the use thereof , other versions , in both structure and use , are contemplated without variance from said principles . it is noted , first of all , that stability in the support of a horizontal structure demands three points . while two pairs have been discussed , it is entirely reasonable to omit one projection , so long as the midpoint of a first linear edge is between two points of support , or projections extending beyond that edge , while a single projection is employed in extension beyond the opposed edge . nor is it necessary to support the shelf along opposed sides . as illustrated in fig4 adjacent sides of the standard grocery cart by horizontal frame members upon a single vertical elevation is quite practical . in this case , naturally , at least one projection 7 , or means of support , is necessary extending from the perimeter , or along adjacent sides , of the main body 3 of the shelf . a triangular configuration is depicted as the simplest illustration of a structure adhering to this embodiment of the principle relating to the present invention , but any configuration possessing horizontal balance will suffice . it is also noted that the perimeter of any structure in adherence to the principles of the present invention need not be straight , or linear , but this is considered the most efficacious for the intended purpose of the current invention . similarly , while it is considered best to construct a shelf which is fully removable from a grocery cart , there are at least two configurations possible which admit of an attached shelf which would not inhibit unduly the horizontally nesting character of the standard design of grocery carts prevalent in the united states today . specifically , a shelf may be attached to a horizontal frame member 6 along either a side or the front vertical wall of such a cart . this attachment is illustrated in fig5 wherein at least one and preferably two projections 7 extending beyond the perimeter of the main body 3 of the shelf possess an arcuate portion 17 of appropriate radius and sufficient length to engage a rod comprising a horizontal frame member 6 along either a side or the front vertical wall of a standard grocery cart . in this case , it is considered that the front wall is preferred over a side wall in deference to the horizontally nesting character of these carts , however , either deployment is equivalent in regard to the principles relating to the present invention . if a shelf in accordance with the present invention is attached by means providing a pivot about a horizontal frame member of the cart basket , as illustrated in fig5 it is furthermore considered advantageous that the means of support attached to the opposed side or end of the pivot be extensible and or retractable . a linearly extensible and or retractable projection 7 fulfilling such a requirement of such support means is illustrated in fig6 . if this construction is employed for a shelf possessing pivotable attachment to a side wall , the direction of linear extension or retraction is directly opposed to the direction of the projection ( s ) 7 possessing an arcuate portion 17 suitable for attachment to a horizontal frame member 6 . if this feature is employed upon a shelf attached pivotally to the front wall of a cart basket , the direction of extension or retraction is substantially perpendicular to that of the projection ( s ) pivotally attached to a horizontal member along the front vertical wall of the cart basket . it is noted in connection with this feature that pivotally attachment to a horizontal member along a vertical cart basket wall need not be permanent but may be removable as well , as explicitly shown in fig5 and either construction adheres to the principles relating to the present invention . similarly , extension of such means of support opposed to the pivotable attachment of the shelf to a horizontal frame member 6 may be rotatable , as illustrated in fig7 . given a suitable point of attachment to the main body of the shelf , the projection shown here may be rotated inside the exterior perimeter , shown here partially with a first linear edge 1 , of the main body 3 to facilitate positioning of the shelf and rotated outward , beyond the perimeter of the main body in order to rest upon and in communication with the upper surface of a horizontal frame member in order to provide the shelf with means of support . fig8 illustrates a third method of construction of a projection which will facilitate the deployment of a shelf pivotally attached to a horizontal frame member . the projection 7 here depicted possesses a resilience sufficient to permit the projection to pass a horizontal frame member 6 by deflection when positioning the shelf and sufficient rigidity to uphold the load expected during use . in fulfillment of this particular embodiment , it is recommended that a directional resilience opposed to a locking rigidity be practiced . tension spring loading of the projection in a linear direction combined with a pivot permitting vertical displacement , or deflection of the projection , is suggested . in hitting the bottom surface of a horizontal member the directional pivot would effect an extension of the spring and release of the linear lock while contact with the upper surface of a horizontal frame member by the opposite , bottom , surface of the projection would effect the locked position . the preferred method of construction of the main body of the shelf , and of the means of support in the first preferred embodiment of the principles relating to the present invention , is that of a heavy gauge wire grid , similar to that of the standard grocery cart , as mentioned above . alternately , a solid body of plastic or any other material providing a rigid , substantially planar main body is entirely in keeping with said principles . the fixedly attached projections depicted in fig1 - 3 and 5 , as well as the handle depicted in fig3 are also preferably constructed in a heavy gauge wire . if an extensible projection is utilized , the routenier can easily devise an appropriate construction of suitable materials . obviously , wire is preferred also for any projection providing means of pivotable attachment . construction of a grid in heavy gauge wire is normally by standard forming and welding techniques well known to those practiced in the art and no variation from these methods is suggested .