Relation Composition
1. Given sets and relations:
\(R = \{(1,2),(1,3),(2,3),(3,1),(3,3)\}\)
\(S = \{(1,1),(1,3),(2,1),(2,3),(3,2)\}\)
2. First, find the complement of \(R\) over the set \(\{1,2,3\}\times\{1,2,3\}\)
The universal set \(U = \{1,2,3\} \times \{1,2,3\} = \{(x,y) \mid x,y \in \{1,2,3\}\}\) with 9 elements.
3. The complement of \(R\), denoted \(\overline{R}\), is all pairs in \(U\) that are not in \(R\):
\[
\overline{R} = U \setminus R = \{(1,1), (2,1), (2,2), (3,2)\}
\]
4. Compute the composition \(S \circ \overline{R}\):
By definition, \(S \circ \overline{R} = \{(a,c) \mid \exists b: (a,b) \in \overline{R} \text{ and } (b,c) \in S\}\).
5. Find all such pairs:
- For \(a=1\), check \((1,b) \in \overline{R}\): \((1,1)\) only.
Find \((1,c) \in S\) where \(b=1\): \((1,1), (1,3)\).
So pairs \((1,1), (1,3)\) in composition.
- For \(a=2\), check \((2,b) \in \overline{R}\): \((2,1), (2,2)\).
For \(b=1\), \(S\) has \((1,1), (1,3)\).
For \(b=2\), \(S\) has none (since no \((2,c)\) present in S? Actually, \(S\) has \((2,1), (2,3)\), so we should correct that).
For \(b=1\), pairs: \( (2,1) \to (1,1), (1,3) \Rightarrow (2,1), (2,3) \)
For \(b=2\), pairs: \( (2,2) \in \overline{R} \) and \((2,1), (2,3) \in S\) so \((2,1), (2,3)\) also in composition.
Wait, the composition requires \((a,b) \in \overline{R}\) and \((b,c) \in S\).
So for \(a=2\), \(b=1\) or \(2\).
\((1,c) \in S\) are \((1,1), (1,3)\);
\((2,c) \in S\) are \((2,1), (2,3)\).
So from \(b=1\): \((2,1)\) implies \((2,1), (2,3)\) composition pairs.
From \(b=2\): \((2,1), (2,3)\) composition pairs.
Actually, for \(b=1\), \(S\) maps to \(c=1,3\) so \((2,1), (2,3)\) included.
For \(b=2\), \(S\) maps to \(1,3\) as well. So from \((2,2)\) in \(\overline{R}\), composing with \(S\) gives \((2,1), (2,3)\).
So total for \(a=2\): \((2,1), (2,3)\).
- For \(a=3\), \(\overline{R}\) pairs: \((3,2)\).
\(S\) pairs starting with \(2\): \((2,1), (2,3)\).
So composition pairs: \((3,1), (3,3)\).
6. So \(S \circ \overline{R} = \{(1,1), (1,3), (2,1), (2,3), (3,1), (3,3)\}\).
7. Finally, find the inverse \(T = (S \circ \overline{R})^{-1} = \{(y,x) \mid (x,y) \in S \circ \overline{R} \}\):
\[
T = \{(1,1), (3,1), (1,2), (3,2), (1,3), (3,3)\}
\]
8. Writing \(T\) in Python set notation:
\texttt{T = \{(1,1), (3,1), (1,2), (3,2), (1,3), (3,3)\}}