Definition:Set Product/Family of Sets

Definition

Let $\family {S_i}_{i \mathop \in I}$ be an indexed family of sets.

Let $P$ be a set.

Let $\family {\phi_i}_{i \mathop \in I}$ be an indexed family of mappings $\phi_i: P \to S_i$ for all $i \in I$ such that:

For all sets $X$ and all indexed families $\family {f_i}_{i \mathop \in I}$ of mappings $f_i: X \to S_i$ there exists a unique mapping $h: X \to P$ such that:

$\forall i \in I: \phi_i \circ h = f_i$

that is, such that for all $i \in I$:

$\quad \quad \begin {xy} \xymatrix@+1em@L+3px { X \ar@{-->}[d]_*+{h} \ar[dr]^*+{f_i} \\ P \ar[r]_*{\phi_i} & S_i } \end {xy}$

is a commutative diagram.

Then $P$, together with the family of mappings $\family {\phi_i}_{i \mathop \in I}$, is called a product of (the family) $\family {S_i}_{i \mathop \in I}$.

This product of $\family {S_i}_{i \mathop \in I}$ can be denoted $\struct {P, \family {\phi_i}_{i \mathop \in I} }$.

Also see

• Definition:Cartesian Product of Family
• Definition:Product (Category Theory)/General Definition

• Results about set products can be found here.

Sources

• 1975: T.S. Blyth: Set Theory and Abstract Algebra ... (previous) ... (next): $\S 6$. Indexed families; partitions; equivalence relations