NETMaths

Is this true?

Cauchy's theorem applies to any domain without singularities of f

No — it is false.

The counterexample

f(z) = 1/z on the annulus ½ < |z| < 2

f is holomorphic there but dz — the annulus is not simply connected.

The kind of mistake this is

Standard counterexample

There is a canonical object that settles this. Recognising it is the whole question.

Drill statements like this

Others that fail the same way

From Cauchy TheoryCauchy's theorem and integral formula

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