definiens: shall mean, with respect to any TYSABRITransaction:(A)if the aggregate Net Sales for the calendar year endingimmediately prior to the consummation of such TYSABRITransaction was less than or equal to two billion dollars($2,000,000,000 ), eighteen percent ( 18 % ) ; or(B)if the aggregate Net Sales for the calendar year endingimmediately prior to the consummation of such TYSABRITransaction was more than two billion dollars($2,000,000,000 ), the amount ( expressed as a percentage)obtained by dividing ( x ) the sum of three hundred and sixtymillion ( $ 360,000,000 ) and twenty - five percent ( 25 % ) of theamount by which the aggregate Net Sales for the calendaryear ending immediately prior to the consummation of suchTYSABRI Transaction exceeds two billion dollars($2,000,000,000 ) by ( y ) the aggregate Net Sales for thecalendar year ending immediately prior to such TYSABRITransaction