Table:
text: Men's pole vault world record progression
Record Progression
Record Progression
Record Athlete Nation Venue Date_
6.03 m Sergey Bubka Soviet Union Prague , Czechoslovakia June 23, 1987
6.05 m Sergey Bubka Soviet Union Bratislava , Czechoslovakia June 9, 1988
6.06 m Sergey Bubka Soviet Union Nice , France July 10, 1988
6.07 m Sergey Bubka Soviet Union Shizuoka , Japan May 6, 1991
6.08 m Sergey Bubka Soviet Union Moscow , Soviet Union June 9, 1991
6.09 m Sergey Bubka Soviet Union Formia , Italy July 8, 1991
6.10 m Sergey Bubka Soviet Union Malmö , Sweden August 5, 1991
6.11 m Sergey Bubka Ukraine Dijon , France June 13, 1992
6.12 m Sergey Bubka Ukraine Padua , Italy August 30, 1992

Question: What is the nation among the world records in the men's pole vault with a date that is May 6, 1991?