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Four things to know for the week ahead

Here's your briefing on some of the most important and interesting stories happening in the week ahead:

1. El Chapo goes on trial
Mexican drug kingpin Joaquín "El Chapo" Guzmán goes on trial in New York City on Tuesday. The trial could last up to four months.

Why does it matter?
There is a case to be made that El Chapo is the most powerful person to be prosecuted in modern times. He is certainly among the richest.

He headed up the Sinaloa drug cartel in Mexico, which became the world's most powerful drug trafficking gang and dominated the heroin, cocaine and methamphetamine trade into the US.

The cartel made up to $3bn (£2.3bn) a year and had influence in at least 50 countries.

El Chapo escaped twice from prison and was finally caught in 2016, then extradited to the US. He's also accused of being behind the killing of rivals and witnesses, so security in court will be extremely tight.

Read the full story here

2. Italy to agree budget
Italy has struggled to agree its budget for months, and faces a deadline of Tuesday to do so.

Why does it matter?
This isn't just an issue that could affect Italy, but Europe and the world as well.
Italy is governed by a coalition of populist far-right and far-left parties, who had made various spending promises during their campaigns.
But the country's debt is already worryingly high - equivalent to 131% of the country's GDP, the second-highest figure in the eurozone after Greece.
Read the background to this here

3. Is a Kilogram really a Kilogram...
From this week, the kilogram may no longer weigh a kilogram. Sort of.

Why does it matter?
There are few certainties in life, but you would have thought this was one of them.
It turns out what we think of as a kilogram has been based, for all this time, on a Perfect Kilogram, the Kilogram To End All Kilograms, that is made of platinum and iridium and kept in a nice jar in Paris.
Unlike us humans though, the thing known as the International Prototype Kilogram has been losing weight as it has been getting older.
It's been losing only a tiny amount, but it's not really clear why, so now scientists are to meet this week to discuss a new way to accurately define what a kilogram is, using electromagnetism.
Will this redefinition change all our lives?
No, but it's interesting.

Read more about this here

4. British Passport holders... will we need a visa to visit EU?
A decision will be taken on Tuesday on whether British passport holders will need a visa to visit the EU after Brexit.

Why does it matter?
The European Commission could decide British people will need permission to travel to EU countries after 29 March 2019, a requirement that usually applies to countries in the developing world.
If this is the case, Britons would have to fill in a three-page form, pay €60 (£52; $68) for a visa and wait up to six weeks for approval. Romantic last-minute trips on the Eurostar would become a thing of the past.
French President Emmanuel Macron suggested last month that Brits travelling to France wouldn't need visas in the event of no Brexit deal being agreed between the UK and Europe.
But will his European partners agree?