MATH0050 - 2021-2022 first assessment
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MATH0050
Answer all (five) questions .
1.
Below, x, y represent variable symbols, P represents a unary predicate symbol and Q represents a binary predicate symbol.
(a) Consider the following strings in Lstring :
) Qxy ) ¬PxPy ) Px
))) Px¬¬QxyPyAxPx
For each of these strings, determine whether or not it is a formula in L. (b) Convert the following formula of Lmath to a formula in L:
((Qxy) , ((3y)(Py))) ) (Py) (20 marks)
2.
Below, ↵ , β , γ are taken to be distinct primitive propositions.
(a) For each of the following, use the semantic tableaux method to determine whether or not the given semantic implication holds. If a semantic implication does not hold, describe every (type of) valuation for which it fails to hold.
(i) {(↵ , β) ^ (¬γ)} |= γ ) (↵ ) β)
(ii) {γ ) (↵ ) β)} |= (↵ , β) ^ (¬γ)
(b) Determine, without constructing truth tables or further semantic tableaux, whether or not the following syntactic implication holds:
{(¬γ) ^ (↵ , β) , γ} ` ↵ ) β
Justify your answer; you may quote, without proof, any relevant results from our course. (20 marks)
3.
Below, ↵ , β , γ , 6 are taken to be propositions.
(a) Give a direct proof of the following:
{↵ ) (β ) (¬γ)) , ↵ ) β} ` ↵ ) (¬γ)
(b) Use the Deduction Theorem for propositional logic to show the following: {↵ ) (¬ (β ) γ)) , (¬6) ) (β ) γ)} ` ↵ ) 6
(c) Determine whether or not the following set of propositions is consistent: {¬(γ ) β) , β} (20 marks)
4.
(a) Describe a theory, in a suitably defined first order predicate language L(⇧, ⌦), such that a structure U is a (normal) model of the theory if and only if U is a group of order 5 i .e . a group containing exactly 5 elements .
(b) Describe a theory, in a suitably defined first order predicate language L(⇧, ⌦), such that a structure U is a (normal) model of the theory if and only if U is a graph consisting of at most 7 vertices and in which there exist at least two vertices each of which is not connected, by an edge, to any vertex .
(c) Does there exist a theory in a suitably defined first order predicate language L(⇧, ⌦), such that a structure U is a (normal) model of the theory if and only if U is a graph consisting of a countably infinite number of vertices?
Justify your answer; you may quote, without proof, any relevant results from our course . (20 marks)
5.
(a) For each of the following functions, show that the function is recursive:
(i) h1 : N0(2) ! N0 , h1 (m,n) = 4
(ii) h2 : N0(2) ! N0 , h2 (m,n) = (m + 4)n
(b) For each of the following functions, determine whether or not the function is computable:
g1 : N0(2) ! N0 , g1 (m,n) = 4m2 n
g2 : N0 ! N0 , g2 (n) = 4n3 +5
Justify your answers; you may quote, without proof, any relevant results from our course . (20 marks)
2023-05-05