Collapsible binders and the like

In a collapsible support structure the combination with a cover formation including a stiff central panel portion of generally uniform quadrilateral perimetral configuration arranged so as to present upper, lower and side edges and a pair of stiff side panel portions flanking said central panel portion and hingedly connected thereto along opposite side edges for swinging movement from a fully closed position with side panel portion in opposed relation to a substantially fully extended open position in side-by-side coplanar relation with said stiff central panel portion and reversely, of means for supporting said cover formation in inclined relation from below with said aforementioned panel portions disposed in substantially fully extended open position, said supporting means including stiff central strut means having upper lower and side edges hingedly interconnected adjacent its upper edge to said central panel portion to swing from a position thereagainst to a substantially upright position therebelow and shiftable stiff side strut means extending between each side panel portions of said cover and said central strut means and interengageable means presented by said shiftable side strut means and said side panel portions respectively to each other for interengaged relative sliding movement therebetween upon swinging movement from said fully closed position to said fully extended open position and reversely and for releasably anchoring same against displacement when said side panel portions are disposed in substantially coplanar side-by-side inclined relation with said stiff central panel portion.