I have encountered the equilibrium concept of "Stackelberg leader-leader equilibrium" while reading Product Line Rivalry (AER, Brander and Eaton (1984). They say "we define a Stackelberg strategy as one which involves taking into account the contemporaneous reaction of one's rival in setting one's own strategy". That definition does not really help me.
Does anyone have a reference or an explanation ? Of course, Google only returns results on the leader-follower game.