MATH 314 THE SYMMETRIC GROUP HOMEWORK 1
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MATH 314 THE SYMMETRIC GROUP
HOMEWORK 1
Problem 1. Consider Z(N) = {0, 1, ..., N - 1}. Suppose χ : Z(N) → C \ {0} is a function such that
χ(m + n) = χ(m)χ(n) for all m, n e Z(N).
Show that we must have χ = ee for some l = 0, 1, 2, ..., N - 1.
(Hint: first show χ(0) = 1. Then determine what values are possible for χ(1) .
Problem 2. a) For ee1 and ee2 instances of the functions we have defined on Z(N), find a
simple formula for
in terms of l) and l1 . (Recalling ee (n) = ei1πen/N may be helpful.)
b) Prove for f, g : Z(N) → C,
Problem 3. Let σ be the permutation 3 4 5 2 1 (in one line notation), and let τ be the permu- tation 5 3 2 4 1. Write the following permutations in cycle notation: σ, τ, σ 1 , στ, τσ .
Problem 4. Prove that sn is generated by the n - 1 transpositions (1 2), (1 3), ..., (1 n).
Problem 5. Use one-line notation to write a permutation π = x) x1 . . . xn e sn . An inversion is a pair of (xi , xj ) such that i < j and xi > xj . Let inv[π] be the number of inversions of π. (So for instance 3 4 5 2 1 has inversions (3, 2), (3, 1), (4, 2), (4, 1), (5, 2), (5, 1), (2, 1) and inv[3 4 5 2 1] = 7.)
a) Show that if π can be written as a product of k transpositions, then k 三 inv[π] (mod 2).
b) Show that the sign of a permutation π is well-defined.
2022-01-25