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Abel's theorem in problems and solutions - School of Mathematics

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84 Chapter 2<br />

294. Suppose the variation <strong>of</strong> the argument along a curve be<br />

equal to <strong>and</strong> be the cont<strong>in</strong>uous image <strong>of</strong> the curve under the<br />

mapp<strong>in</strong>g F<strong>in</strong>d the variation <strong>of</strong> the argument along the curve<br />

295. F<strong>in</strong>d the branch po<strong>in</strong>ts <strong>of</strong> the function<br />

In §2.5 we have used the notation<br />

<strong>and</strong> we have considered some properties <strong>of</strong> this complex number.<br />

296. Suppose that a curve does not pass through the po<strong>in</strong>t<br />

<strong>and</strong> that is one <strong>of</strong> the cont<strong>in</strong>uous images <strong>of</strong> the curve under<br />

the mapp<strong>in</strong>g F<strong>in</strong>d all the cont<strong>in</strong>uous images <strong>of</strong> the curve<br />

under the mapp<strong>in</strong>g<br />

Suppose that two curves <strong>and</strong> jo<strong>in</strong> a po<strong>in</strong>t to a different po<strong>in</strong>t<br />

Exactly as <strong>in</strong> the case <strong>of</strong> function (cf., 284), one proves that if<br />

the curve does not turn around the po<strong>in</strong>t then the function<br />

is uniquely def<strong>in</strong>ed by cont<strong>in</strong>uity along the curves <strong>and</strong> In this<br />

way if, as for the function we make a cut from the po<strong>in</strong>t to<br />

<strong>in</strong>f<strong>in</strong>ity the image <strong>of</strong> the function turns out to be decomposed<br />

<strong>in</strong>to s<strong>in</strong>gle-valued cont<strong>in</strong>uous branches.<br />

297. Make a cut from the po<strong>in</strong>t to <strong>in</strong>f<strong>in</strong>ity, not pass<strong>in</strong>g through<br />

the po<strong>in</strong>t <strong>and</strong> def<strong>in</strong>e the s<strong>in</strong>gle-valued cont<strong>in</strong>uous branches <strong>of</strong> the<br />

function by the conditions: where takes the <strong>in</strong>teger<br />

values from 0 to How are the branches expressed <strong>in</strong> terms <strong>of</strong><br />

298. Draw the scheme <strong>of</strong> the Riemann surface <strong>of</strong> the function<br />

299. F<strong>in</strong>d the branch po<strong>in</strong>ts <strong>and</strong> draw the scheme <strong>of</strong> the Riemann<br />

surface for the function<br />

300. F<strong>in</strong>d the branch po<strong>in</strong>ts <strong>and</strong> draw the scheme <strong>of</strong> the Riemann<br />

surface <strong>of</strong> the function<br />

When a multi-valued function has several branch po<strong>in</strong>ts, <strong>in</strong> order to<br />

separate the s<strong>in</strong>gle-valued cont<strong>in</strong>uous branches we make the cuts from<br />

every branch po<strong>in</strong>t to <strong>in</strong>f<strong>in</strong>ity along l<strong>in</strong>es which do not <strong>in</strong>tersect each<br />

other.<br />

In this way the scheme <strong>of</strong> the Riemann surface <strong>of</strong> a given function<br />

may depend essentially on the choice <strong>of</strong> the cuts from the branch po<strong>in</strong>ts

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