Prefabricated staircase structure

Claim 1

A STAIRCASE COMPRISING AT LEAST ONE STRINGER AND A PLURALITY OF PREFABRICATED STEP MEMBERS ENGAGEABLE FROM ABOVE WITH SAID STRINGER AT LOCATIONS REGULARLY SPACED ALONG SAID STRINGER AND EXTENDING TRANSVERSELY WITH RESPECT TO THE LATTER, AND STRINGER INCLUDING AN ELONGATED CHANNEL MEMBER HAVING DOWNWARDLY CONVERGING SIDES AND A BOTTOM WEB EXTENDING BETWEEN SAID SIDES AND HAVING TRANSVERSELY ELONGATED SLOTS IN SAID WEB AT LOCATIONS SPACED APART ALONG THE STRINGER, EACH OF SAID STEP MEMBERS INCLUDING A BASE HAVING DOWNWARDLY CONVERGING SIDES ENGAGEABLE WITH SAID SIDES OF THE CHANNEL MEMBER TO TRANSVERSELY LOCATE THE STEP MEMBER WITH RESPECT TO SAID STRINGER WHEN BEING LOWERED ONTO THE LATTER, SAID BASE OF EACH STEP MEMBER FURTHER HAVING A FLAT-WEBBED HOOK EXTENDING FROM THE BOTTOM OF SAID BASE AND OPENING FORWARDLY BELOW THE LATTER SO AS TO BE GUIDED TRANSVERSELY INTO STEPSECURING ENGAGEMENT WITH ONE OF SAID SLOTS BY THE INTERENGAGEMENT OF SAID SIDES OF THE BASE AND CHANNEL MEMBER WHEN A STEP MEMBER IS LOWERED ONTO THE STRINGER, AND MEANS ON EACH STEP MEMBER INTERLOCKING WITH THE NEXT LOWER STEP MEMBER ON SAID STRINGER TO PREVENT MOVEMENT OF SAID NEXT LOWER STEP MEMBER IN THE DIRECTION FOR DISENGAGING SAID FLAT-WEBBED HOOK FROM THE SLOT OF SAID BOTTOM WEB IN WHICH IT IS ENGAGED.