 (Note: “f(y)” here may be pronounced “the f of y”.) For example: if we say that the identity of a marriage depends on the identities of the two people being married, if x is a marriage and y and z are the two people in question, (ID-NEC) is satisfied in respect of x and y in virtue of the fact that x is necessarily identical with the marriage of y with z—so that in this case the required function is the marriage with z function from persons to events. (We here ignore the complications created by the fact that, under some legal systems, the same two persons may be married to one another more than once.) However, (ID-NEC) turns out to be unsatisfactory as a definition, because it can be regarded as trivially true, given standard set theory, that any x and y that may be connected with a function will satisfy the consequent of (ID-NEC). So we better find a more satisfactory definition of identity-dependence.