Must the price and the preempted share be known for the preemption to be valid?

Primary text

If the price (*thaman*) or the preempted share (*shaqs*) is unknown, the pre-emptor does not gain ownership through the taking expression. This is because preemption is in essence a sale, and therefore knowledge of the two considerations (price and item sold) is required, as in all other sales contracts. The pre-emptor has the right to demand preemption first and then ascertain the price from the buyer or another party, taking the property at its established price.