Retractable ladder

Claim 1

A RETRACABLE LADDER COMPRISING, A PLURALITY OF INTERENGAGING SLIDEABLY ATTACHED INTERMEDIATE AND ADJACENT LADDER SECTIONS, EACH SECTION COMPRISING A PAIR OF LATERALLY SPACED PARALLEL LONGITUDINALLY EXTENDING STRINGER MEMBERS AND UNIFORMLY LONGITUDINALLY SPACED TRANSVERSELY EXTENDING TREAD MEMBERS SECURED AT THEIR OPPOSITE ENDS TO SAID STRINGER MEMBERS, SAID STRINGER MEMBERS BEING OF CHANNEL SHAPED CROSS-SECTION TO PROVIDE IN EACH INSTANCE A WEB AND PARALLEL SIDE FLANGES AND THE STRINGER MEMBERS OF SUCCESSIVE SECTIONS BEING TURNED 180* WITH THE FLANGES OF THE STRINGER MEMBERS OF SAID INTERMEDIATE SECTION POSITIONED WITHIN THE CHANNELS OF THE STRINGER MEMBERS OF SAID ADJACENT SECTIONS THEREBY PROVIDING TELESCOPIC ENGAGEMENT OF SAID SECTIONS FOR MOVEMENT BETWEEN RETRACTED AND EXTENDED POSITIONS, SAID LADDER BEING ADAPTED FOR MOUNTING IN A VERTICALLY INCLINED ATITUDE IN ITS EXTENDED POSITION AND SAID SECTIONS BEING FORMED IN SUCH POSITION TO PLACE ALL OF THE TREAD MEMBERS BEING OF INVERTED SECTION IN HORIZONTAL JUXTAPOSITION TO TREAD MEMBERS OF ADJACENT SECTIONS, SAID TREAD MEMBERS BEING OF INVERTED CHANNEL SHAPED CROSS-SECTION TO PROVIDE A FLAT TOP WEB AND DEPENDING SIDE FLANGES, THE LOWER ENDS OF ONE OF SAID FLANGES OF EACH OF SAID TREADS BEING SPACED FROM ONE OF SAID FLANGES OF THE ATTACHED STRINGER MEMBER TO PROVIDE A GUIDEWAY SLIDEABLE RECEIVING THE FLANGE OF THE TELESCOPICALLY ATTACHED STRINGER MEMBER, SAID TOP WEBS OF SAID JUXTAPOSED TREAD MEMBERS BEING POSITIONED IN SAID EXTENDED INCLINED POSITION OF THE LADDER IN HORIZONTAL CO-PLANAR RELATION TO COOPERATIVELY PROVIDE A FLAT HORIZONTAL DOUBLE WIDTH TREAD.