| Two other reasons, also sufficient by themselves, is that neither 3 nor 4 are first elements input of any ordered pair therein | Hughes-Hallett, Deborah; Connally, Eric; McCallum, William G |
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| Lord, Nick, "Golden bounds for the roots of quadratic equations", Mathematical Gazette 91, November 2007, 549 |
One reason is that 2 is the first element in more than one ordered pair, 2, B and 2, C , of this set.
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