D4XN ...[??? STEPBAC1 SECT CENT FGN 9 DOC   
 D57G    # THIS MACRO IS A MORE CONVENIENT FORM OF STEPBAC   
 D5M6    #MAC  STEPBAC1 [JSRAYNER.STEPBACK ONR   
 D66Q          MACCS    %A,%B
 D6LB          STEPBAC  0
 D762    #NOR