Ben, c'est pourtant la première chose qui est dite dans le gatherer:
Citation :
12/1/2004 Trinisphere's ability affects the total cost of the spell. It is applied *after* any other cost increasers or cost reducers are applied: First apply any cost increases. Next apply any cost reducers. Finally look at the amount of mana you have to pay. If it's less than three mana, you'll pay three mana.