@Garibaldino:
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Not sure about the real meaning of c) rule in comparison with a) and b)
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Welcome to the forum, Garibaldino.
A major industrial complex (MIC) can produce 10 units. Their maximum damage is 20. So far, so good.
Now your point c) comes in:
In case the damage of a MIC is exactly 10 no unit can enter the game and you need to repair at least 1 damage to allow 1 unit to enter.
Repair 10 to allow 10 units to enter the game - or any number inbetween.
If the damage is 11, you need to repair 2 damage to allow 1 unit to enter the game.
If the damage is 20, you need to repair 11 damage to allow 1 unit to enter the game.
So this is the meaning of the sentence “Industrial complexes can have at least as many damage markers as they have production ability. In such a case, no new units can enter the game through that complex until it’s repaired.”
Please ask, if anything remains unclear :-)