The value of PRB is derived on the date of the deal finally go through. So, in theory, PRB's value is whatever .1755 the value of each goldcorp share is worth on the date the deal goes through plus the value of the New PRB. Therefore, as goldcorp stock goes up or down, the corresponding value of PRB goes up or down. For example, if goldcorp is worth $35 on the day it goes through, PRB is worth 6.14 plus whatever value the market gives new prb. Traders looking for arbitrage opportunities are looking to get PRB at a price less than the .1755 plus the new prb value.