Could be general, or the semifinal. Murray controls his own destiny to an extent.
1. Djokovic is top of his group and will play the runner up of the Murray group in the semifinal no matter what he does today in the round robin against Goffin.
2. Thiem and Raonic control their own destiny and whomever wins their next round-robin match tonight will play the winner of the Murray group in the semifinal.
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3. Andy vs Stan tomorrow in the afternoon. If Andy beats Stan, Andy is top of his group and will play the winner of Thiem-Raonic in the semifinal, Nishikori will be runner-up and play Novak Djokovic in the SF.
4. If Stan beats Andy, and Cilic beats Nishikori, Stan is top in the group and will play the winner of Thiem-Raonic,and Andy is second.
5. If Stan beats Andy, and Nishikori beats Cilic, then it gets more complicated:
a. If Stan wins in 2 sets, and Nishikori beats Cilic, then Andy is out completely and Stan is in. If that happened, Nishikori will be top in the group if he wins in 2 sets, Stan runnerup, or if Nishikori wins in 3 sets then Stan is top in group and Nishikori is runnerup.
b. Even if Stan wins in 3 sets, if Nishikori beats Cilic, then Stan is out completely and Murray will be top in group if Nishikori wins in 3 sets and Kei will be runnerup. Or if Nishikori wins in 2 sets, Kei will be top in group and Andy will be runnerup.
I found this picture that might show it more clearly General:

Respectfully,
masterclass