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Show that each of these conditional statements is a tautology using logical equivalences.a) (๐‘ โˆง ๐‘ž) โ†’ ๐‘b) ยฌ๐‘ โ†’ (๐‘ โ†’ ๐‘ž)c) (๐‘ โˆง ๐‘ž) โ†’ (๐‘ โ†’ ๐‘ž)

Question

Show that each of these conditional statements is a tautology using logical equivalences.

a) (๐‘ โˆง ๐‘ž) โ†’ ๐‘

b) ยฌ๐‘ โ†’ (๐‘ โ†’ ๐‘ž)

c) (๐‘ โˆง ๐‘ž) โ†’ (๐‘ โ†’ ๐‘ž)

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Solution

Sure, let's go through each of these conditional statements one by one:

a) (๐‘ โˆง ๐‘ž) โ†’ ๐‘

This statement can be rewritten using the logical equivalence of the conditional statement, which is ยฌ๐‘ โˆจ ๐‘ž. So, (๐‘ โˆง ๐‘ž) โ†’ ๐‘ becomes ยฌ(๐‘ โˆง ๐‘ž) โˆจ ๐‘.

Using De Morgan's law, ยฌ(๐‘ โˆง ๐‘ž) can be rewritten as ยฌ๐‘ โˆจ ยฌ๐‘ž. So, ยฌ(๐‘ โˆง ๐‘ž) โˆจ ๐‘ becomes (ยฌ๐‘ โˆจ ยฌ๐‘ž) โˆจ ๐‘.

Using the associative law, we can rearrange this to ยฌ๐‘ โˆจ (ยฌ๐‘ž โˆจ ๐‘).

Finally, using the law of disjunction (which states that ๐‘ โˆจ ยฌ๐‘ is always true), we can see that (ยฌ๐‘ž โˆจ ๐‘) is always true, and therefore the entire statement is a tautology.

b) ยฌ๐‘ โ†’ (๐‘ โ†’ ๐‘ž)

This statement can be rewritten using the logical equivalence of the conditional statement, which is ยฌ๐‘ โˆจ (๐‘ โ†’ ๐‘ž).

The inner conditional statement (๐‘ โ†’ ๐‘ž) can also be rewritten using the logical equivalence of the conditional statement, which gives us ยฌ๐‘ โˆจ (ยฌ๐‘ โˆจ ๐‘ž).

Using the associative law, we can rearrange this to (ยฌ๐‘ โˆจ ยฌ๐‘) โˆจ ๐‘ž.

Finally, using the law of idempotency (which states that ๐‘ โˆจ ๐‘ is equivalent to ๐‘), we can simplify this to ยฌ๐‘ โˆจ ๐‘ž.

Since ยฌ๐‘ โˆจ ๐‘ž is always true (because either ๐‘ is false, or ๐‘ is true and ๐‘ž is true), the entire statement is a tautology.

c) (๐‘ โˆง ๐‘ž) โ†’ (๐‘ โ†’ ๐‘ž)

This statement can be rewritten using the logical equivalence of the conditional statement, which is ยฌ(๐‘ โˆง ๐‘ž) โˆจ (๐‘ โ†’ ๐‘ž).

Using De Morgan's law, ยฌ(๐‘ โˆง ๐‘ž) can be rewritten as ยฌ๐‘ โˆจ ยฌ๐‘ž. So, ยฌ(๐‘ โˆง ๐‘ž) โˆจ (๐‘ โ†’ ๐‘ž) becomes (ยฌ๐‘ โˆจ ยฌ๐‘ž) โˆจ (๐‘ โ†’ ๐‘ž).

The inner conditional statement (๐‘ โ†’ ๐‘ž) can also be rewritten using the logical equivalence of the conditional statement, which gives us (ยฌ๐‘ โˆจ ยฌ๐‘ž) โˆจ (ยฌ๐‘ โˆจ ๐‘ž).

Using the associative law, we can rearrange this to ยฌ๐‘ โˆจ (ยฌ๐‘ž โˆจ (ยฌ๐‘ โˆจ ๐‘ž)).

Finally, using the law of disjunction (which states that ๐‘ โˆจ ยฌ๐‘ is always true), we can see that (ยฌ๐‘ž โˆจ (ยฌ๐‘ โˆจ ๐‘ž)) is always true, and therefore the entire statement is a tautology.

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