Let (sn) be a sequence that converges.
(a) Show that if sn ≥ a for all but finitely many n,
then lim sn ≥ a.
(b) Show that if sn ≤ b for all but finitely many n,
then lim sn ≤ b.
(c) Conclude that if all but finitely many sn belong to [a,b],
then lim sn belongs to [a, b].
1) a) Let k ≥ 2 and let G be a k-regular bipartite
graph. Prove that G has no cut-edge. (Hint: Use the bipartite
version of handshaking.)
b) Construct a simple, connected, nonbipartite 3-regular graph
with a cut-edge. (This shows that the condition “bipartite” really
is necessary in (a).)
2) Let F_n be a fan graph and Let a_n = τ(F_n) where τ(F_n) is
the number of spanning trees in F_n. Use deletion/contraction to
prove that a_n = 3a_n-1 - a_n-2...
Let sn = 21/n+ n sin(nπ/2), n ∈ N.
(a) List all subsequential limits of (sn).
(b) Give a formula for nk such that (snk) is an unbounded
increasing subsequence of (sn).
(c) Give a formula for nk such that (snk) is a convergent
subsequence of (sn).
Let S = {2 k : k ∈ Z}. Let R be a relation defined on Q− {0} by
x R y if x y ∈ S. Prove that R is an equivalence relation.
Determine the equivalence class
Let k be an integer satisfying k ≥ 2. Let G be a connected graph
with no cycles and k vertices. Prove that G has at least 2 vertices
of degree equal to 1.
Abstract Algebra
Let n ≥ 2. Show that Sn is generated by each of the
following sets.
(a) S1 = {(1, 2), (1, 2, 3), (1, 2, 3, 4), ..., (1,
2, 3,..., n)}
(b) S2 = {(1, 2, 3, ..., n-1), (1, 2, 3, ..., n)}
Let sn be a Cauchy sequence such that ∀n > 1, n ∈ N, ∃m >
1, m ∈ N such that |sn − m| = 1/3 (this says that every term of the
sequence is an integer plus or minus 1/3 ). Show that the sequence
sn is eventually constant, i.e. after a point all terms of the
sequence are the same