DISCRETE MATH: Express the following using propositions p,q,r and logical connectives

1. Jan 9, 2007

VinnyCee

1. The problem statement, all variables and given/known data

Express the system specifications using the propositions p "The user enters a valid password," q "Access is granted," and r "The user has paid the subscription fee" and logical connectives.

a) The user has paid the subscription fee, but does not enter a valid password.

b) Access is granted whenever the user has paid the subscription fee and enters a valid password.

c) Access is denied if the user has not paid the subscription fee.

d) If the user has not entered a valid password but has paid the subscription fee, then access is granted.

2. Relevant equations

p = "The user enters a valid password"
q = "Access is granted"
r = "The user has paid the subscription fee"

3. The attempt at a solution

a) $$r\,\wedge\,\neg\,p$$

b) $$q\,\longleftrightarrow\,(r\,\wedge\,q)$$

c) $$\neg\,r\,\longrightarrow\,\neg\,q$$

d) $$(\neg\,p\,\wedge\,r)\,\longrightarrow\,q$$

2. Jan 9, 2007

Everything looks right, except you made a typo (I guess) in b), it should be $$q\,\longleftrightarrow\,(r\,\wedge\,p)$$, unless I'm missing something.

3. Jan 9, 2007

matt grime

Even modulo typos, b is not right. The implication is not both ways. It does not assert that the only way to get access is with subscription and a valid password.

4. Jan 9, 2007

Excuse my mistake, it should be $$(r \wedge p) \Rightarrow q$$.

5. Jan 9, 2007

VinnyCee

So they are all right except that B is really $$(r\,\wedge\,p)\,\longrightarrow\,q$$?

6. Jan 10, 2007