A filled torus (a doughnut) is a 3-manifold homeomorphic to \(S^1 \times D^2\), where \(D^2\) is the 2-dimensional disk. There exists a deformation retract from the doughnut to a circle, so the fundamental group of the doughnut is \(\pi_1(S^1 \times D^2) \cong \mathbb{Z}\).
And she's watched plenty of astronauts follow in her footsteps. Does she have any advice for the next generation dreaming of the stars?
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These fees can be wild. When my PhD advisor and I published one of our papers together, the journal charged us an “open access” fee of $12,000. This arrangement is a tiny bit better than the alternative, because at least everybody can read our paper now, including people who aren’t affiliated with a university. But those fees still have to come from somewhere, and whether you charge writers or readers, you’re ultimately charging the same account—namely, the US government.5。同城约会对此有专业解读
Зеленскому стали чаще желать смерти02:42，这一点在体育直播中也有详细论述