First and second U-shaped cross-members each have legs connected by cross bars and pivotally connected with each other at central portions thereof, and are mutually movable from a generally X-shaped setup condition in which the cross bars are transversely spaced apart, to a generally flat collapsed condition. Right and left frame side assemblies respectively are pivotally connected to the first and second cross-members at terminal ends of their respective front and rear portions and by at least one lost motion linkage.
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