Let the universal set be the set of all files in MyDocuments. What about choosing the collection of predicates, e.g., E(x) means "x is envrypted"? Can you do that?
please help with the following problem
Consider the following statements:
Every file in MyDocuments is encrypted or hidden. Every encrypted
file in MyDocuments is secure. Every secure file in MyDocuments
contains secrets. There is a file in MyDocuments which does not contain
secrets. Therefore there is a file in MyDocuments which is hidden.
Choose an appropriate universal set and collection of predicates, and express this argument in the language of predicate calculus.
i am trying the problem. please check if its ok or not.
U, the set of all files in MyDocuments
we define the following functions
E(x), indicates if file x is encrypted
H(x), indicates if file x is hidden
Secure(x), indicates if file x is secure
Secret(x), indicates if file x contains secrets
we can now write the given statements using predicate and logical connectives
∀x ∈ U: E(x) ∨ H(x)
∀x ∈ U: E(x) ⇒Secure(x)
∀x ∈ U: Secure(x) ⇒ Secret(x)
∃x ∈ U: ¬( Secret(x) ) ⇒ ∃x ∈ U: H(x)
I agree with what you wrote, except that the last line looks like one formula, i.e., one assumption. The claim to be proved should be clearly separated from all the assumptions.
Let us know if you need help with constructing a formal or informal derivation, etc.
Emakarov meant that this should be clear for everybody who reads your text. Thus I suggest you write it for example like this
In this form the readers can see which are the givens and what the conlcusion is.
Yes, that was my idea.
If one wants to express the whole problem as one formula (for example, in order to feed it to an automatic theorem prover and see if it is derivable), then the long implication given by OP is also correct. I would only put extra parentheses to avoid ambiguity and possibly add some indentation, something like this:
(∀x ∈ U: (E(x) ∨ H(x))) ∧
(∀x ∈ U: (E(x) ⇒ Secure(x))) ∧
(∀x ∈ U: (Secure(x) ⇒ Secret(x))) ∧
(∃x ∈ U: ¬(Secret(x))) ⇒
∃x ∈ U: H(x)
Bloody editor: I don't know how to indent the last line by a couple of spaces.