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Why Read This Book? - Index of

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1.3 Universal and Existential Quantifiers 31<br />

(a) There is a function in F whose graph intersects the x-axis.<br />

(b) No function in F has a graph that intersects the x-axis.<br />

(c) There is a function in F whose graph does not intersect the x-axis.<br />

Sometimes a universal statement might be expressed informally by placing<br />

the ∀ phrase after the property that is universally true. <strong>This</strong> is merely a way to<br />

make a sentence sound more natural. We would not write the statement that way<br />

symbolically. The next example illustrates this with a range <strong>of</strong> expressions from<br />

informal to formal.<br />

Example 1.3.10 The following statements are equivalent.<br />

There is an element <strong>of</strong> set A that is less than every element <strong>of</strong> set B.<br />

There exists x ∈ A such that x

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