Jerome Singleton (USA), Alan Fonteles Oliveira (Brazil), Oscar Pistorius (South Africa) and Blake Leeper (USA).
I had mixed feelings when I watched Oscar Pistorius make history in London as the first amputee to compete against able-bodied runners at the Olympics.
I was full of admiration for the 25-year-old South African - how could you not be?
Pistorius was born without fibulas. His legs were amputated below the knee before he was a year old.
He won four Paralympic gold medals, but he always longed to compete at the Olympics, and appeared at countless inquiries to win the right to do so.
He finally took his place in London, where he made the 400 metres semi-finals and ran in a relay.
It's an inspiring story. But I had concerns about the wisdom of allowing him to compete, for one reason: no matter which way you look at it, it wasn't an even playing field.
Either he was at a disadvantage because he was running on carbon fibre blades, instead of legs, or he was at an advantage for the same reason. But there's no way it could be the same.
That's why they have the Paralympics. But even there, organisers run into problems categorising the athletes and drawing up rules designed to make things fair for all.
Lo and behold, Pistorius ran again in the Paralympics in London this week, was beaten for the first time ever in a 200-metre race, then promptly complained that the winner had an unfair advantage because of his prosthetics.
Pistorius claimed that Brazilian Alan Oliveira's carbon fibre legs were too long. This made him taller than he should be, allowing him to take longer strides and gain an unfair edge.
Pistorius made the same claim against the T44 race bronze medallist, American Blake Leeper, saying his knee height was 10 centimetre more than it should be.
There are rules stipulating that the prosthetic limbs should make the athlete as tall as he would be if he had legs, but it seems this is a grey area.
"We're not racing a fair race here," said Pistorius.
"Not taking away anything from Alan's performance - he's a great athlete - but these guys are a lot taller and you can't compete with the stride length. "The guys are just running ridiculous times."
If there were no rules governing the height or composition of prosthetics, sports scientists would probably soon be devising attachments with optimum length and weight ratios, and no doubt fitting them with springs.
It's always the same when equipment becomes as important in sport as the people who use it.
Is the Formula One motor racing championship won by the best driver or the best car? Is the America's Cup won by the best yacht or the best sailors?
Sport is always at its most riveting, and fairest, when the competitors are separated only by human qualities like ability, endeavour, preparation, experience, strategy and tactics.
The Pistorius controversy reminded me of a New Zealand woman called Neroli Fairhall, who took up archery after a car accident put her in a wheelchair. In 1984 she became the first paraplegic to compete at the Olympics, and at the Brisbane Commonwealth Games two years earlier she won gold in blustery conditions.
Some disgruntled rivals suggested the wheelchair gave her an advantage through having a lower centre of gravity and greater stability in the wind.
To which she replied with disarming candour: "I don't know. I've never shot standing up."
