Question: What profession do both Lucie Šafářová and Sergio Casal share?

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1991 Athens Open – Doubles: Sergio Casal and Javier Sánchez were the defending champions, but Casal did not participate this year.  Sánchez partnered Goran Prpić, losing in the first round.

Sergio Casal: Sergio Casal Martínez (born 8 September 1962) is a former professional tennis player from Spain.  During his career, he won three Grand Slam doubles titles, as well as the men's doubles Silver Medal at the 1988 Summer Olympics.

Lucie Šafářová career statistics: This list summarizes the main career statistics of Czech professional tennis player Lucie Šafářová.  To date, Šafářová has won seven WTA singles titles and fifteen WTA doubles titles including five Grand Slam doubles titles with Bethanie Mattek-Sands at the 2015 Australian Open and French Open,; the 2016 US Open and 2017 Australian Open and French Open.  Other highlights of Šafářová's career thus far include winning the 2015 Qatar Total Open, reaching the final of the 2015 French Open and making quarterfinal and semifinal appearances at the 2007 Australian Open and 2014 Wimbledon Championships, respectively.  Šafářová achieved career high singles and doubles rankings of World No. 5 and World No. 2 on 14 September 2015 and 30 January 2017.

2014 Family Circle Cup – Doubles: Kristina Mladenovic and Lucie Šafářová were the defending champions, but Mladenovic chose not to participate this year.  Šafářová played alongside Květa Peschke, but they lost in the first round to Chan Hao-ching and Chan Yung-jan.

Lucie Šafářová: Lucie Šafářová (] ; born 4 February 1987) is a Czech professional tennis player from Brno.  She is currently the WTA world No. 1 doubles player.  Šafářová has won seven WTA tour singles titles, fifteen doubles titles and reached the quarterfinals of the 2007 Australian Open by upsetting defending champion Amélie Mauresmo in the fourth round.  She reached her first Grand Slam semifinal at the 2014 Wimbledon Championships and her first Grand Slam final at the 2015 French Open.  She also won the 2015 Australian Open, 2015 French Open, 2016 US Open, 2017 Australian Open and 2017 French Open women's doubles titles partnering with Bethanie Mattek-Sands.

2016 Rogers Cup – Women's Doubles: Bethanie Mattek-Sands and Lucie Šafářová were the defending champions, but decided not to compete together.  Mattek-Sands played alongside Heather Watson, but lost in the quarterfinals to Andreja Klepač and Katarina Srebotnik.  Šafářová teamed up with Tímea Babos, but lost in the first round to Kateryna Bondarenko and Olga Savchuk.

2016 Porsche Tennis Grand Prix – Doubles: Bethanie Mattek-Sands and Lucie Šafářová were the defending champions, but Mattek-Sands chose not to participate this year.  Šafářová played alongside Sabine Lisicki, but lost in the semifinals to Martina Hingis and Sania Mirza. <br>

2017 US Open – Women's Doubles: Bethanie Mattek-Sands and Lucie Šafářová were the defending champions, but Mattek-Sands was unable to compete due to injury.  Šafářová played alongside Barbora Strýcová, but lost in the semifinals to Lucie Hradecká and Kateřina Siniaková.

2016 Australian Open – Women's Doubles: Bethanie Mattek-Sands and Lucie Šafářová were the defending champions, but Šafářová withdrew before the tournament due to a bacterial infection.  Mattek-Sands played alongside Sabine Lisicki, but lost in the second round to Anastasia and Arina Rodionova.

2015 Apia International Sydney – Women's Doubles: Tímea Babos and Lucie Šafářová were the defending champions, but chose not to participate together.  Babos played alongside Kristina Mladenovic, but lost in the semifinals to Raquel Kops-Jones and Abigail Spears.  Šafářová teamed up with Belinda Bencic, but lost in the first round to Kimiko Date-Krumm and Karolína Plíšková. <br>

Supporting paragraphs: Lucie Šafářová Sergio Casal
Answer: professional tennis player