Premise: The 1987 Federation Cup was the 25th edition of the most important competition between national teams in women 's tennis . The Grand Slam tournaments , also called majors , are the four most-important annual tennis events . 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 . The Women 's Doubles competition was part of the tennis program at the 1988 Summer Olympics .
Hypothesis: Steffi Graf is incapable of being a tennis player.
Label: CONTRADICTION