the roof of the building was supposed to be made up of large concrete sails - a visually arresting but logistically very tricky plan. An even more ambitious design, with flatter sails, had already been ruled out.

What it needed was a strong arch that would be able to support exactly the amount of pressure from the concrete. So he set to work.

Bertony spent the next half a year working on the calculations for that arch support, solving 30,000 different complex equations by hand. Those notes, which are now on display in Sydney's Museum of Applied Arts and Sciences, were all neatly and methodically laid out.

"He was a brilliant mathematician," Ms Pitt says. "He did those 30,000 hand-rendered mathematical equations in six months, which is a very short period of time - and that's all he did. He would eat, breathe and sleep the Sydney Opera House."

Ms Pitt says that occasionally, despite years having passed, he would still be in awe of what he had helped to create.

"The last time I drove with him across the Harbour Bridge, he glanced over to the right to the opera house as he was driving and said: 'I still can't believe I did that.'"