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Space Race
Defend Earth from alien invaders
Sequence
a function whose domain is the natural numbers

converges
a sequence (aⁿ)→a (a real number) if, for every positive number ∈, there exists an N∈of the natural numbers such that whenever n≥N it follows that |aⁿ-a|<∈

∈-neighborhood of a
Given a real number a∈R and a positive number ∈≥0, the set V₋(a)={x∈R: |x-a|<∈}

Diverge
a sequence that does not converge

eventually
a sequence (aⁿ) is _________ in a set A⊆R if there exists an N∈N such that aⁿ∈A ∀n≥N

frequently
a sequence (aⁿ) is __________ in a set A⊆R if, for every N∈N, there exists an n≥N such that aⁿ∈A

bounded
a sequence (xⁿ) is _______ if there exists a number M>0 such that |xⁿ|≤M for all n∈N.

increasing
a sequence (aⁿ) is ________ if aⁿ< aⁿ⁺¹ for all n∈N

decreasing
a sequence (aⁿ) is ________ if aⁿ>aⁿ⁺¹ for all n∈N

subsequence
Let (aⁿ) be a sequence of real numbers, and let n₁<n₂<n₃<... be an increasing sequence of natural numbers. Then the sequence aⁿ₁,aⁿ₂,aⁿ₃,....is a _______

Cauchy sequence
a sequence (aⁿ) is called a ________ if, for every ∈>0, there exists an N∈N such that whenever m,n≥N it follows that |aⁿ -aⁿⁿ| <∈

open
A set O⊆R is ______ if for all points a∈O there exists and ∈-neighborhood V₃(a) ⊆ O.

limit point
A point x is a _____________of a set A if every ∈-neighborhood V₃(x) of x intersects the set A in some point other than x.

isolated point
A point a∈A is an ____________ of A if it is not a limit.

closed
A set F⊆R is _______ if it contains its limit points

closure
Given a set A⊆R, let L be the set of all limit points of A. The _________ of A is defined to be A = A ∪ L.

compact
A set K⊆R is ________ if every sequence in K has a subsequence that converges to a limit that is also in K.

bounded
A set A⊆R is __________ if there exists M > 0 such that |a| ≤ M for all a∈A.

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