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Question

Let A be the set of all functions $f: Z \to Z$ and R be a relation on A such that $R = \{(f, g) : f(0) = g(1) \text{ and } f(1) = g(0)\}$. Then R is :

The correct answer is
Symmetric but neither reflective nor transitive

Analyzing the Relation R on Functions

We are given a set A of all functions $f: \mathbb{Z} \to \mathbb{Z}$ and a relation R defined as:

$R = \{(f, g) \in A \times A \mid f(0) = g(1) \text{ and } f(1) = g(0)\}$

We need to determine if R is reflexive, symmetric, and transitive.

Relation Properties Check

Reflexivity

A relation R is reflexive if $(f, f) \in R$ for every function $f \in A$. This requires $f(0) = f(1)$ and $f(1) = f(0)$ for all $f$.

Consider the function $f(x) = x$. Here, $f(0) = 0$ and $f(1) = 1$. Since $f(0) \neq f(1)$, the condition $f(0) = f(1)$ is not met.

Therefore, R is not reflexive.

Symmetry

A relation R is symmetric if $(f, g) \in R$ implies $(g, f) \in R$.

Assume $(f, g) \in R$. This means:

  • $f(0) = g(1)$
  • $f(1) = g(0)$

Now, let's check the conditions for $(g, f) \in R$:

  • We need $g(0) = f(1)$. From our assumption, $f(1) = g(0)$, which is true.
  • We need $g(1) = f(0)$. From our assumption, $f(0) = g(1)$, which is true.

Since both conditions are met, if $(f, g) \in R$, then $(g, f) \in R$.

Therefore, R is symmetric.

Transitivity

A relation R is transitive if $(f, g) \in R$ and $(g, h) \in R$ implies $(f, h) \in R$.

Assume $(f, g) \in R$ and $(g, h) \in R$. This means:

  1. $f(0) = g(1)$
  2. $f(1) = g(0)$
  3. $g(0) = h(1)$
  4. $g(1) = h(0)$

We need to check if $(f, h) \in R$, which requires $f(0) = h(1)$ and $f(1) = h(0)$.

From the assumptions:

  • Combining (1) and (4): $f(0) = g(1) = h(0)$. This gives $f(0) = h(0)$.
  • Combining (2) and (3): $f(1) = g(0) = h(1)$. This gives $f(1) = h(1)$.

The conditions derived ($f(0) = h(0)$ and $f(1) = h(1)$) are not the required conditions for $(f, h) \in R$ (which are $f(0) = h(1)$ and $f(1) = h(0)$).

Let's use a counterexample:

  • Let $f(x) = x$. Then $f(0)=0, f(1)=1$.
  • Let $g(x) = 1-x$. Then $g(0)=1, g(1)=0$. $(f, g) \in R$ because $f(0)=0=g(1)$ and $f(1)=1=g(0)$.
  • Let $h(x) = x$. Then $h(0)=0, h(1)=1$. $(g, h) \in R$ because $g(0)=1=h(1)$ and $g(1)=0=h(0)$.
  • Now check $(f, h)$: We need $f(0) = h(1)$ and $f(1) = h(0)$.
  • Here, $f(0) = 0$ and $h(1) = 1$. Since $0 \neq 1$, $f(0) \neq h(1)$.
  • Thus, $(f, h) \notin R$.

Therefore, R is not transitive.

Conclusion

Based on the analysis:

  • R is not reflexive.
  • R is symmetric.
  • R is not transitive.

The relation R is symmetric but neither reflexive nor transitive.

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