Collapsible ladder

Claim 1

A LADDER COMPRISING A PLURALITY OF SUBSTANTIALLY EQUAL SECTIONS, EACH SECTION INCLUDING TWO TUBULAR SIDE BARS AND A RUNG, A PAIR OF HINGES EACH INCLUDING TWO HINGE ELEMENTS, RESPECTIVELY SECURED TO A PAIR OF ADJACENT BAR ENDS OF ADJOINING SECTIONS, EACH HINGE ELEMENT INCLUDING A FLANGE AND A FOOT, SAID RUNG CONSTITUTING THE HINGE AXLE AND BEING PASSED THROUGH SAID FLANGES AND AXIALLY NON-SHIFTABLY SECURED TO AT LEAST ONE OF SAID HINGE ELEMENTS SO AS TO MAINTAIN A PREDETERMINED SPACING OF THE BARS OF EACH SECTION, THE FOOT OF EACH HINGE ELEMENT BEING OF CONCAVE SHAPE SO AS TO ENCOMPASS A PORTION OF THE CROSS-SECTION OF THE ASSOCIATED BAR, A PORTION OF THE FOOT OF EACH HINGE ELEMENT OF ONE OF SAID ADJOINING SECTIONS PROJECTING FROM THE END OF THE ASSOCIATED BAR IN THE LONGITUDINAL DIRECTION THEREOF, AND THE ADJOINING BAR END PROJECTING FROM THE FOOT OF ITS ASSOCIATED HINGE ELEMENT AND BEING ADAPTED TO ENGAGE IN SAID PROJECTING FOOT PORTION SO THAT THE LATTER CONSTITUTES A BED FOR THE PROJECTING BAR END WHEN THE BARS ARE ALIGNED, AND A LOCKING MEANS TO HOLD ADJOINING BARS IN ALIGNED POSITION WHEN TURNED INTO SAID POSITION ABOUT THE HINGE AXIS, SAID LOCKING MEANS INCLUDING A HOOK MEMBER AND A PIN MEMBER, ONE OF SAID MEMBERS BEING SECURED TO THE END OF ONE OF SAID ADJACENT BARS INTERIORLY THEREOF, SAID OTHER MEMBER BEING MOVABLE HELD WITHIN THE OTHER ONE OF SAID ADJACENT BARS SO AS TO PROJECT THEREFROM, A SPRING BEARING ON SAID OTHER MEMBER AND TENDING TO MOVE IT INTO ENGAGEMENT WITH SAID FIRST MEMBER WHEN SAID ADJACENT BARS ARE ALIGNED, AND A LEVER OUTSIDE OF SAID OTHER BAR AND IN COOPERATIVE RELATIONSHIP TO SAID SECOND MEMBER TO MOVE THE LATTER OUT OF ENGAGEMENT WITH SAID FIRST MEMBER.