28 lines
615 B
Markdown
28 lines
615 B
Markdown
Page 512
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**Definition**
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Let $R$ be a relation from $A$ to $B$. Define the inverse relation $R^{-1}$ from
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$B$ to $A$ as follows:
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$$ R^{-1} = \{(y, x) \in B \times A | (x, y) \in R\} $$
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---
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Page 513
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**Definition**
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A **relation on a set** A is a relation from $A$ to $A$.
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---
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Page 514
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**Definition**
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Given sets $A_1, A_2, \dots, A_n$ an **$n$-ary relation** $R$ on
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$A_1 \times A_2 \times \cdots \times A_n$ is a subset of
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$A_1 \times A_2 \times \cdots \times A_n$. The special cases of $2$-ary,
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$3$-ary, and $4$-ary relations are called **binary**, **ternary**, and
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**quarternary relations**, respectively.
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