Mordell-Weil groups of a hyperk\"ahler manifold - a question of F.   Campana
  Mordell-Weil groups of different abelian fibrations of a hyperk\"ahler manifold may have non-trivial relation even among elements of infinite order, but have essentially no relation, as its birational transformation. Precise definition of the terms "essentially no relation" will be given in Introduction. 
Keiji Oguiso