35324 LC Mathematical and Logical Foundations of Computer Science 2022
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06-35324
35324 LC Mathematical and Logical Foundations of Computer Science
Main Summer Examinations 2022
Question 1
(a) Numbers and sets
(i) Compute 42 and 43 modulo 3 . From these results, conjecture a property P(n) of 4n modulo 3 . Prove by induction that P(n) is satisfied for all n e N .
[3 marks]
(ii) Let sqr t : {x e N | x > 0} → {y e R | y > 0} be the square root function
from non-negative integers to non-negative reals, i .e . sqr t(x) = y if and only if x = y2 .
Is sqr t injective? surjective? bijective? Justify your answers . [3 marks]
(iii) Let float javaSqrt(int x) be a Java implementation of this square root
function (assume it throws an exception if x is negative) . Discuss the differ- ences between sqr t and javaSqrt when considered as mathematical functions between sets . [4 marks]
(b) Linear algebra
Consider the three points
P1 = (2(1)) (4l
P2 = ( -0(1))
( 4 l
P3 = ( -2(1))
( 2 l
(i) Show that these form the corners of an equilateral triangle (i .e . a triangle where all sides have the same length) . [2 marks]
(ii) The triangle defines a plane M in R3 . Give its parametric representation and
its normal form . [4 marks]
(iii) Another plane N is given by
( 0(1)) (1(1)) (0(2))
Find the line of intersection of M and N .
Show your working for each part .
[4 marks]
Question 2
(a) Propositional Logic
Let F be the formula (A V B) → (B V A), and
let G be the formula A → (B → (-B V -A)) → -B .
(i) Provide a constructive Sequent Calculus proof of F .
(ii) Provide a constructive Natural Deduction proof of G .
(iii) Is G satisfiable? Justify your answer .
[4 marks]
[6 marks]
[2 marks]
(b) Predicate Logic
Consider the following signature:
❼ Function symbols: zero (arity 0); succ (arity 1)
❼ Predicate symbols: < (arity 2); < (arity 2)
We will use infix notation for the binary symbols < and <. Consider the following formula that captures a property of the above symbols:
❼ let S1 be Ax .-(x < 0)
For simplicity we write 0 for zero, 1 for succ(zero), 2 for succ(succ(zero)), etc .
(i) Provide a constructive Natural Deduction proof of:
S1 - -3x .Ay .x < y
[4 marks]
(ii) Provide a model M1 such that 卡M1 -(Ax .Ay .x < y - x < y), and a model M2
such that 卡M2 Ax .Ay .x < y - x < y [4 marks]
2022-08-15