Picking the starting eleven at Barcelona is no longer a spur-of-the-moment tactical call. Under Hansi Flick, it has become a precise mathematical equation, applied with rigour.
Flick has publicly declared this the most balanced squad since his arrival, and from the first whistle of the season he has run a rotation system that leaves nothing to chance. That same system may now hand us his line-up against Racing.
Six official matches in, five in La Liga and one in the Champions League, the pattern has become clear, according to "Mundo Deportivo".
Two starting teams share the dressing room, an equation that has delivered dazzling results so far. If the German sticks to it tomorrow, Wednesday, against Racing, then it will be the turn of Koundé, Christensen, Cancelo, Olmo and Adjemi.
The rotation rule in Barcelona's defence
At right-back, Eric García and Jules Koundé take it in turns. The La Masia graduate started against Athletic Bilbao, Valencia and Levante, while the Frenchman got his chance against Rayo Vallecano and Feyenoord. His absence in one match came down to suspension.
Central defence follows the same rule. Gerard Martín started against Athletic Bilbao, Valencia and Levante, while Andreas Christensen, who featured in the opener against Elche to cover for the absent Cubarsí, started against Rayo Vallecano and Feyenoord.
On the left, the rotation ran between Baldé, who started against Valencia and Levante, and Cancelo, who came in from the start against Feyenoord.
Midfield and attack: no one rests except Pedri and Lamine
In defensive midfield, Marc Bernal and Fermín López or Rodri swapped roles. Bernal started the first three, against Elche, Athletic Bilbao and Rayo Vallecano, while his teammate took charge of the last three against Valencia, Feyenoord and Levante. Only Pedri escapes the churn. He remains an indispensable starter.
Further forward, Fermín and Olmo rotate. The former started against Athletic Bilbao, Valencia and Levante, the latter got the nod against Rayo and Feyenoord.
Out wide, Lamine Yamal is a permanent fixture on the right, but the left has seen rotation in the last three matches between Gordon, who started in La Liga against Valencia and Levante, and Adjemi, who started against Feyenoord and Elche.
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The substitutions confirm the German theory
The equation shows up in the substitutions too, not just the starting line-up. When Gordon and Adjemi come off the bench, they keep swapping roles, as happened against Elche, Rayo, Valencia, Feyenoord and Levante. The same scenario plays out between Bernal and Rodri.
Flick's equation knows no favours. Everyone plays, and everyone is ready.