Premise: Stefanie Maria `` Steffi '' Graf ( [ ˈʃtɛfiː ˈgʁa : f ] ; born 14 June 1969 ) is a German former tennis player , who was ranked world No. 1 during her career . Furthermore , she is the only tennis player to have won each Grand Slam event at least four times . Graf was ranked world No. 1 by the Women 's Tennis Association ( WTA ) for a record 377 total weeks -- the longest period for which any player , male or female , has held the number-one ranking since the WTA and the Association of Tennis Professionals began issuing rankings .
Hypothesis: Steffi Graf is an amateur tennis player.
Label: CONTRADICTION