1:14 PM
specific-question This question has been bumped recently: Three half circles on the plane may not meet nicely. It has two deprecated tags and I am not sure whether other tags are suitable. (Why at.algebraic-topology belong here? I am not sure about linear-algebra either? What about adding discrete-geometry?
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Let $H$ denote the union of the northen hemisphere of the unit circle $S^{1}$ with the interval $[-1,1]$ on the $x$-axis. That is, $H=\{(x,\sqrt{1-x^{2}}):-1\le x\le 1\}\cup\{(x,0):-1\le x\le 1\}$ Let us say that two copies of $H$ meet nicely if they intersect in exactly 6 points e.g. as the two...
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