When playing with Halicarnassus A side and I build a second wonder stage, is it possible to build a structure that in its precondition cost has another structure which a player controlling Halicarnassus doesn't have built?
For example, to build Haven, you need to have a Forum in play.
There are no building prerequisites. The building names next to the cost indicate that you may construct the building for free, without having to fulfill the resource cost. From the rulebook, p. 4:
Free Construction (Chains): Some structures in Age II and Age III have, to the right of their resource cost, the name of a structure of a previous age. If the player has built the structure named there during a previous Age, that player can build the structure for free, meaning without having to fulfill the resource cost.
Since Halikarnassos allows you to construct any building in the discard pile for free, anyway, the "chained" card is irrelevant at that point. Nevertheless, you are still forbidden from constructing a duplicate card.
