Two or more @[email protected] are said to be concerted (or to constitute a concerted process) if they occur within the same @[email protected] Such changes will normally (though perhaps not inevitably) be 'energetically coupled'. (In the present context the term 'energetically coupled' means that the simultaneous progress of the primitive changes involves a @[email protected] of lower energy than that for their successive occurrence.) In a concerted process the primitive changes may be @[email protected] or asynchronous.