There is a foreign-key $F$ in Relation1 that references set of attributes $G$ of Relation2. Suppose a tuple $t$ of Relation1 has non-NULL values in all the attributes of $F$, call the list of $t$'s values in these attributes $t[F]$, then in Relation2 there must be some tuple that ____ with $t[F]$ on the attributes $G$.