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Hello and welcome to more or less on the BBC World Service with me, Charlotte MacDonald.

In this week's programme, we discussed the work of the British mathematician Sir Andrew Wiles,

who's found a solution to a 300-year-old mathematical mystery

and secured the prestigious Arbal Prize for his efforts.

But first, London has a newly elected mayor, Sadiq Khan.

In the aftermath of his election victory, he named London the most

diverse and fantastic city in the world. But is he right? Is it really the most diverse city?

Here's more or less is roving reporter Ed Davie.

It's certainly a very diverse city.

In the Dollis Hill area of North London, for example, white British people account for just 14% of the population.

And of the 11 other ethnic groups that make up the population there, the largest is Indian at 11%.

So it's a real old mix-up.

The most recent count in 2014 found that

37% of Londoners were born outside of the UK. Is that how you measure the diversity of a city,

the percentage born in a different country? Well, diversity is tricky to measure, so people have

often looked at the proportion born in a foreign country as an easy way to compare different cities.

But it is a technique with flaws.

For a start, it doesn't catch second or third generation immigrants.

Sadiq Khan's election was meant to be a display of diversity, but he was actually born in London,

...