= Plumbing of oriented disk bundles
Plumbing identifies a base disk times a fiber disk in one oriented rank-two <disk bundle> with such a neighborhood in another, exchanging base and fiber coordinates. Their zero sections then intersect transversely once. For disk bundles over $S^2$ arranged along a chain with Euler numbers $-a_i$, the <intersection form> has diagonal entries $-a_i$, adjacent entries one and other entries zero. The same manifold has a <Kirby diagram> consisting of adjacent Hopf-linked unknots with framings $-a_i$. Its boundary is described by the corresponding <negative continued fraction>, with the orientation fixed by the surgery convention.
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