ATP Finals: Could the permutations be any more complicated?

Players in the ATP Finals — All four players in Group Lleyton Hewitt can still mathematically qualify for the semi-finals of the ATP Finals in London

ATP Finals
Venue: O2 Arena, London Dates: 11-18 November
Coverage: Follow live coverage across BBC TV, radio, the BBC Sport website & mobile app. Live text commentary available on selected matches.

Does your brain hurt trying to work out the permutations for the ATP Finals?

Roger Federer beat Dominic Thiem on Tuesday to keep alive his hopes of making it through to the semi-finals at the 02 Arena in London.

But whether or not he will qualify remains complicated.

Here's how people reacted on social media after the ATP tweeted this graphic:

'My brain hurts'

Some of you just replied with emojis of confused faces.

But many of you responded with funny gifs including this one from Abel Morton.

And this one from Roger Buchana.

Though most of you just said what we were all thinking...

Optimist: I have a headache!

Marcou: I'm lost!

Adeyanju Michael: This is Maths :(

Aditya Jain: Don't understand anything.

N Kessler: My brain hurts.

So, is there an easy way to understand it?

In short, no.

Here's our attempt at a 'simple' breakdown of how the top two are decided in each of the two four-player groups:

Greatest number of wins
If two players are tied: Head-to-head results
If three players are tied: 1) Highest percentage of sets won; 2) Highest percentage of games won; 3) Players' ATP Rankings coming into the tournament

So with that in mind, Federer will go through if any of these situations happen:

He wins in two sets and Thiem beats Kei Nishikori in two.
He wins in two sets and Thiem wins in three.
He wins in two sets and Nishikori beats Thiem in two sets. Highest % of games won will then be the decider.
He wins in two sets and Nishikori wins in three.
He wins in three sets and Thiem wins in two.
He wins in three sets and Thiem wins in three.

This is how the group currently stands:

Group Lleyton Hewitt
	P	W-L	Sets	Games
Kevin Anderson	2	2-0	4-0	25-10
Kei Nishikori	2	1-1	2-2	14-21
Roger Federer	2	1-1	2-2	21-18
Dominic Thiem	2	0-2	0-4	14-25

If you're still not sure what's going on, the best thing to do is to follow our guide on the group standings, results and fixtures and just trust us when we say Federer is through or not.