In general , this need not be nonzero because , for formula 9 in formula 10 , formula 11 in formula 12 and any injective formula 13 in formula 14 .
In general , this need not be injective because , for formula _ 9 in formula _ 10 , formula _ 11 in formula _ 12 and any nonzero formula _ 13 in formula _ 14 ,