= Two-handle
{title2=$D^2\times D^{n-2}$}
A <two-handle> on an $n$-dimensional <manifold with boundary> is $D^2\times D^{n-2}$ attached along $S^1\times D^{n-2}$. Its <attaching sphere> is a circle, and its <framing> specifies the neighbouring normal disks. In <dimension> four, this is a framed <knot> in the three-dimensional boundary. On the <fundamental group>, the attachment kills the element represented by the attaching circle, together with its normal closure. Different framings can give different resulting <manifolds> even when the attaching circle is fixed.
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