Let X be a finite set on which G acts, let ρ be the corresponding permutation representation [cf. 1.2, example (c)], an...
14&15 13 Let o be a permutation of a set A. We shall say "o moves a € A" if o(a) are moved by a cycle o E SA of length n? a. If A is a finite set, how many elements 14 Let A be an infinite set. Let H be the set of all o ESA such that the number of elements moved by o is finite. Show that H is a subgroup of SA
4. If G is a group, then it acts on itself by conjugation: If we let X = G (to make the ideas clearer), then the action is Gx X = (g, x) H+ 5-1xg E G. Equivalence classes of G under this action are usually called conjugacy classes. (a) If geG, what does it mean for x E X to be fixed by g under this action? (b) If x E X , what is the isotropy subgroup Gx...
Let a ∈ G where G is a group. If X ⊆ G is a finite subset, write Xa = {xa | x ∈ X}. Show that X and Xa have the same number of elements.
(10 pts) Let G be a finite group acting on a set X. Prove that the he number of orbits equals the quantity Σ9EG points of G. #4 X where for g G, X9 denotes the number of fixed (10 pts) Let G be a finite group acting on a set X. Prove that the he number of orbits equals the quantity Σ9EG points of G. #4 X where for g G, X9 denotes the number of fixed
Let X be a finite set and F a family of subsets of X such that every element of X appears in at least one subset in F. We say that a subset C of F is a set cover for X if X =U SEC S (that is, the union of the sets in C is X). The cardinality of a set cover C is the number of elements in C. (Note that an element of C is a...
Always give rigorous arguments I. (A) Let G be a group under * and let g E G with o(g) = n (finite) (i) Show that g can never go back to any previous positive power of g* (1k< n) when taking up to the nth power (cf. g), e., that there are no integers k and m such that 1< k<m<n and such that g*-gm (ii) How many elements of the set (e, g,g2.... .g"-) are actually distinct? (iii)...
5. Let X1,X2, . , Xn be a random sample from a distribution with finite variance. Show that (i) COV(Xi-X, X )-0 f ) ρ (Xi-XX,-X)--n-1, 1 # J, 1,,-1, , n. OV&.for any two random variables X and Y) or each 1, and (11 CoV(X,Y) var(x)var(y) (Recall that p vararo 5. Let X1,X2, . , Xn be a random sample from a distribution with finite variance. Show that (i) COV(Xi-X, X )-0 f ) ρ (Xi-XX,-X)--n-1, 1 # J,...
Problem 7. (20 pts) Let n N be a natural number and X a finite set with n elements. Show that the number of permutations of X such that no element stays in the same position is n. n! k! For instance, there are 6-3! permutations of 3 elements, but only 2 of them are permutations which fix no element. Similarly, there are 24 41 permutations of 4 elements, but only 9 which fix no element Hint: Use the Inclusion-Erclusion...
Problem 7. (20 pts) Let n EN be a natural nmber and X a finite set with n elements. Show that the number of permutations of X such that no element stays in the same position is n! k! k o For instance, there are 6 = 3! permutations of 3 elements, but only 2 of them are permutations which fix no element. Similarly, there are 24-4! permutations of 4 elements, but only 9 which fix no element. Hint: Use...
Let G be a group of order 6 and let X be the set (a, b,c) E G3: abc That is, X is the set of triples of elements of G with the product of its coordinates equals the identity element of G (a) How many elements does X have? Hint: Every triple (a, b, c) in X is completely determined by the choice of a and b. Because once you choose a and b then c must be (ab)-1...