Question: Are both Tom Okker and Kim Clijsters Belgian tennis players?

Context articles: Eva Dyrberg
Ai Sugiyama
Kim Clijsters
Jan Hajer
2003 WTA Tour Championships
Belgium Fed Cup team
Wim Fissette
Clijsters–Henin rivalry
2010 Billie Jean King Cup
Tom Okker

Eva Dyrberg (born 17 February 1980) is a Danish former tennis player.
 As a junior player, she won 1998 Wimbledon Championships with Jelena Kostanić and 1998 US Open with Kim Clijsters.
 In 1998, Dyrberg was also ranked World No. 1 in junior doubles and was named ITF Junior Girls Doubles World Champion.
 During her professional career, she won four singles and five doubles events organized by the International Tennis Federation, defeating players such as Magdalena Maleeva, Tathiana Garbin, Maria Elena Camerin, Nicole Pratt, and reaching one doubles final at WTA Tour, at Sanex Trophy in 2000.
 She retired from professional tennis after the 2003 Australian Open.
Ai Sugiyama (杉山愛 , Sugiyama Ai , born July 5, 1975) is a Japanese former professional tennis player.
 She reached No. 1 in women's doubles on the WTA Tour.
 Her career-high singles ranking was No. 8, achieved on February 9, 2004.
 In her career, she won 6 singles titles and 37 doubles titles, including three Grand Slam women's doubles titles (one with Frenchwoman Julie Halard-Decugis and two partnering Belgian Kim Clijsters).
 Sugiyama held the all-time record, for both male and female players, for her 62 consecutive Grand Slam main draw appearances, until she was surpassed by Roger Federer at the 2015 Wimbledon Championships.
Kim Antonie Lode Clijsters (] ; born 8 June 1983) is a Belgian former professional tennis player.
 Clijsters is a former world No. 1 in both singles and doubles.
Jan Hajer (born 31 March 1942) is a Dutch former tennis player.
 He was national champion in 1963.
 He won the final by winning over Willem Maris, Dutch National Champion in 1962.
 In 1964 Jan Hajer lost the final of the Dutch National Championship against Tom Okker.
 Later Hajer and Okker represented the Netherlands in the Davis Cup team.
 Hajer had a relative short international tennis career and participated in Wimbledon three times.
 In 1967 he reached the second round which he lost in five sets to Jaidip Mukerjea.
 Hajer and Okker competed in doubles events in South Africa, Philippines and Australia.
The 2003 WTA Tour Championships, also known by its sponsored name Bank of America WTA Tour Championships Presented by Porsche, was a women's tennis tournament played on indoor hard courts at the Staples Center in Los Angeles, United States.
 It was the 33rd edition of the year-end singles championships, the 28th edition of the year-end doubles championships, and was part of the 2003 WTA Tour.
 The tournament was held between November 4 and November 10, 2003.
 First-seeded Kim Clijsters won the singles event and earned $1,000,030 first-prize money as well as 485 ranking points.
 With her victory Clijsters became the first female tennis player to earn $US4 million in a season.
 For the first time since 1978 a round robin system was used, after the men's Tennis Masters Cup.
 Two groups of four players were formed and each contender had to play three matches.
 Also, for singles, instead of the top sixteen players qualifying, only top eight qualified for the WTA Tour Championships.
 For doubles, the top four pairs (previously top eight) pairs qualified for the WTA Tour Championships, but still continued with the single elimination format.
The Belgian Fed Cup team, managed by the Belgian Tennis Federation, has been competing in the International Tennis Federation sanctioned Fed Cup since the very beginning: 1963.
 It has won the competition once, in 2001.
 Both Kim Clijsters and Justine Henin won their singles matches to seal the first victory for Belgium against Russia in Madrid.
Wim Fissette (born 22 March 1980) is a Belgian former professional tennis player and current coach, best known for his work with former Women's Tennis Association (WTA) world number ones Victoria Azarenka, Kim Clijsters, former world number two Simona Halep, and, currently, British number one Johanna Konta.
Justine Henin and Kim Clijsters are Belgian professional tennis players who engaged in a long-standing rivalry which spanned twenty-five meetings over a twelve-year period, with eight taking place in a Grand Slam tournament.
 Their final competitive meeting came at the 2010 Wimbledon Championships in the fourth round, with Clijsters winning in 3 sets, this brought their head to head record to 13–12 in Clijsters' favour.
 The Belgians have met eight times in Grand Slam tournaments, three of which were finals.
 Henin leads 5–3 in Grand Slam play including winning all their final match-ups.
The 2010 Billie Jean King Cup was the 2nd edition of this tennis exhibition tournament.
 Seven-time Grand Slam champion Venus Williams, 2009 French Open Champion Svetlana Kuznetsova, and 2009 US Open Champion Kim Clijsters participated.
 2009 Australian Open and Wimbledon Champion Serena Williams had to withdraw from the event due to a leg injury.
 She was replaced by 2008 French Open Champion Ana Ivanovic.
 In the first semifinal, Clijsters defeated Ivanovic in a tiebreaker (7–2), despite Ivanovic having match point at 5–4 up.
 Williams defeated Kuznetsova in the second semifinal, 6–4.
 Williams defeated Clijsters in the championship match by a score of 6–4 3–6 7–5.
Thomas Samuel Okker (born 22 February 1944) is a former Dutch tennis player.
 He was ranked among the world's top 10 singles players for seven consecutive years, 1968–74, reaching a career high of World No. 3 in 1969.
 He also was ranked World No. 1 in doubles in 1969.