= 7. Consider the set Seq[N] of all the infinite sequences (ak)ken = (ao, a₁, a2, a3,...) of natural num- bers. A sequence (ak)ken is constant if there is some number n E N so that ak = n, for all k € N. (a) Construct an injection i: N→ Seq[N]. (b) Prove that there is no surjection f: N → Seq[N]. (Consider the arguments of the proof of Cantor's Theorem that we saw in class.) (c) Deduce from above that No < Seq[N]]. (Actually, it can be proven that Seq[N]| = |R|.)

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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7. Consider the set Seq[ℕ] of all the infinite sequences (a_k)_{k ∈ ℕ} = (a_0, a_1, a_2, a_3, ...) of natural numbers. A sequence (a_k)_{k ∈ ℕ} is constant if there is some number n ∈ ℕ so that a_k = n, for all k ∈ ℕ.

(a) Construct an injection i: ℕ → Seq[ℕ].

(b) Prove that there is no surjection f: ℕ → Seq[ℕ]. (Consider the arguments of the proof of Cantor’s Theorem that we saw in class.)

(c) Deduce from above that ℵ₀ < |Seq[ℕ]|. (Actually, it can be proven that |Seq[ℕ]| = |ℝ|.)
Transcribed Image Text:7. Consider the set Seq[ℕ] of all the infinite sequences (a_k)_{k ∈ ℕ} = (a_0, a_1, a_2, a_3, ...) of natural numbers. A sequence (a_k)_{k ∈ ℕ} is constant if there is some number n ∈ ℕ so that a_k = n, for all k ∈ ℕ. (a) Construct an injection i: ℕ → Seq[ℕ]. (b) Prove that there is no surjection f: ℕ → Seq[ℕ]. (Consider the arguments of the proof of Cantor’s Theorem that we saw in class.) (c) Deduce from above that ℵ₀ < |Seq[ℕ]|. (Actually, it can be proven that |Seq[ℕ]| = |ℝ|.)
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