I'd have to agree with Willyroo's assessment on the fare rules, the example given seems pretty clear. I'm sure plenty of people would be happy if that was a mistaken perception though

*** CX MIXED CLASS(BUSINESS/ECONOMY) TRAVEL O N L Y

O N E SECTOR IN BUSINESS CLASS PERMITTED EITHER FROM HONG KONG TO EUROPE O R V.V.;

O N E SECTOR IN BUSINESS CLASS PERMITTED EITHER FROM AUSTRALIA TO HONG KONG O R V.V.;

E.G. SYD-ECONOMY-HKG-BUSINESS-EUR-ECONOMY-HKG-BUSINESS-SYD).