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This proof is inspired by Diestel (2000). Let G = (V, E) be a simple undirected graph. We proceed by induction on m, the number of edges. If the graph is empty, the theorem trivially holds. Let m > 0 and suppose a proper (Δ+1)-edge-coloring exists for all G − xy where xy ∈ E.
In proof by exhaustion, the conclusion is established by dividing it into a finite number of cases and proving each one separately. The number of cases sometimes can become very large. For example, the first proof of the four color theorem was a proof by exhaustion with 1,936 cases. This proof was controversial because the majority of the cases ...
This proof was hinted at by Aristotle, in his Analytica Priora, §I.23. [12] It appeared first as a full proof in Euclid's Elements, as proposition 117 of Book X. However, since the early 19th century, historians have agreed that this proof is an interpolation and not attributable to Euclid. [13]
Sections 10, 11, 12: Properties of a variable extended to all individuals: section 10 introduces the notion of "a property" of a "variable". PM gives the example: φ is a function that indicates "is a Greek", and ψ indicates "is a man", and χ indicates "is a mortal" these functions then apply to a variable x .
The BEST theorem is due to van Aardenne-Ehrenfest and de Bruijn (1951), [4] §6, Theorem 6. Their proof is bijective and generalizes the de Bruijn sequences.In a "note added in proof", they refer to an earlier result by Smith and Tutte (1941) which proves the formula for graphs with deg(v)=2 at every vertex.
In mathematics and other fields, [a] a lemma (pl.: lemmas or lemmata) is a generally minor, proven proposition which is used to prove a larger statement. For that reason, it is also known as a "helping theorem" or an "auxiliary theorem".
Such a proof is again a refutation by contradiction. A typical example is the proof of the proposition "there is no smallest positive rational number": assume there is a smallest positive rational number q and derive a contradiction by observing that q / 2 is even smaller than q and still positive.
A proof by induction consists of two cases. The first, the base case , proves the statement for n = 0 {\displaystyle n=0} without assuming any knowledge of other cases. The second case, the induction step , proves that if the statement holds for any given case n = k {\displaystyle n=k} , then it must also hold for the next case n = k + 1 ...