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An apparently simple argument put forward by Novak Djokovic, one that seems to make both philosophical and financial sense. Why should female tennis players be paid the same as their male counterparts when fewer spectators want to watch them?
Except equal pay is as much a myth as it is a minefield.
While each of the four Grand Slam tournaments offers the same prize money for men and women (although it took Wimbledon until 2007 and the French Open until 2006, while the US Open had done so as far back as 1973) tennis does not reward its stars in anywhere near the same way.
Djokovic, world number one in 2015, won three of the four Slams last year. He was victorious in 93.18% of his matches. His reward for that, in prize money alone, was £14.5m.
Serena Williams, world number one on the WTA Tour, also won three of the four Slams. She won 94.64% of her matches across the year. Her total prize money? £7.3m.
A little of that disparity came from Djokovic's greater success outside the Slams, and a little more from the fact injury ended Serena's season in October.
But it was not a historical anomaly. In 2014, Williams - again ranked number one - won one Grand Slam, seven titles and the year-end WTA championships. That earned her £6.5m.
Djokovic, also top ranked, won one Grand Slam, seven titles and the year-end ATP championships. He earned £9.9m.
After winning in Indian Wells at the weekend, Djokovic said: "We have much more spectators on the men's tennis matches. I think that's one of the reasons why maybe we should get awarded more."
That, at best, is only a selective argument. Most tennis fans describe themselves as exactly that - lovers of the game, rather than one tour above the other, with the usual partiality for a particular player more likely to be based around their character and on-court style rather than gender.
It is also only selectively true. As Serena pointed out after her final in California: "Last year the women's final at the US Open sold out well before the men."
Djokovic will pick up on stadium attendances because they are there around him as he plays, although the 21st century sporting world is one in which bums on seats contribute far less to finances than television deals.
In the financial year to April 2014, Premier League champions Manchester City made £47m from matchday income - not just tickets, but all revenues at Etihad Stadium during games. From television and broadcasting they earned £133m. Professional tennis follows a similar pattern.
Men's tennis already earns far more from broadcasting rights than the women's game. The latest WTA media deal is worth £365m over 10 years; Stuart Watts, CEO of ATP Media, is forecasting £904m revenues over same period.
That already feeds into the respective prize funds. It is also not a result solely of the popularity of the two tours.
It reflects too a historical cultural predisposition to male sport, the way sports broadcasting is frequently marketed at a predominantly male demographic, how the rest of the mainstream media devotes so much more coverage to men's sport than women's and so influences demand.
If female tennis players are the beneficiaries of the sport's collective bargaining at the biggest events, as some argue within the men's game, then so are many male players.
Djokovic, Roger Federer and Rafael Nadal are all huge draws. People fill arenas to watch them. At the big tournaments they will queue overnight to get tickets.
What of the men they beat? How many of those who sat courtside in Indian Wells on Sunday did so because they wanted to watch Milos Raonic, who Djokovic beat in straight sets?
Men's tennis, just as women's tennis, is not unanimously appreciated. Specific players are, and specific rivalries.
Djokovic, a wonderful player, as relentless in his training and preparation as on court, deserves his success. He is also fortunate his career has overlapped with those of Federer, Nadal and Murray, for it is the intensity and frequency of the battles between those players, rather than their gender, that have made them such a draw.
How many of those who came to the semi-finals at Indian Wells were drawn to see Raonic's defeat of David Goffin, and how many to see Djokovic take on Nadal? Goffin and Nadal left with identical prize money all the same.
Popularity alone can never be the defining factor in how the cake is divided. Had Raonic won this weekend, should he have received less prize money because more spectators had come to watch and support Djokovic? Should Federer have won more than Djokovic at the 2014 Wimbledon final because he had the backing of more of those seated around Centre Court?
If there is an argument about who is paid what in tennis, it might more profitably be focused on the more jarring incongruities - how Maria Sharapova, who has won a grand total of one set in her past 14 matches against Serena, could nonetheless have yearly earnings that dwarf those of the 21-time Grand Slam singles winner.
If there is an argument in tennis to be made about inequity, it should be as much about attitudes as cold cash - about why Serena's dominance of the women's game is frequently described as boring when Djokovic's supremacy on the men's tour is breathtaking; why a series of broken service games in men's tennis is likely to be depicted as a thrilling, see-saw contest while in a women's match it's often blamed on mental flakiness or physical inability.
People watch women's tennis for the contests and the characters, for the skill and the strategies, for the fact we are witnessing the best in their chosen field.
To claim that men should take an even larger proportion of a revenue pool they already dominate would be to denigrate so much of that.
Ignore too the old caveats about how many sets are played, or else Usain Bolt will have to be satisfied with a fraction of the earnings of a marathon runner, and Chris Gayle see a batsman who scores a Test century over seven hours be rewarded in a way that he could not be for doing the same in 47 balls.
Sport is not like most of the industries the rest of us work in. At its basic level it is as meritocratic as is possible: if you are the superior player on that day, you will win.
When you win, you earn more than the player you beat. There lies the simplicity, not elsewhere.