Capped grope

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In mathematics, a grope is a construction used in 4-dimensional topology, introduced by (Štan'ko 1971) and named by (Cannon 1978) "because of its multitudinous fingers". Capped gropes were used by (Freedman 1984) as a substitute for Casson handles, that[vague] work better for non-simply-connected 4-manifolds. A capped surface in a 4-manifold is roughly a surface together with some 2-disks, called caps, whose boundaries generate the fundamental group of the surface. A capped grope is obtained by repeatedly replacing the caps of a capped surface by another capped surface. Capped surfaces and capped gropes are studied in (Freedman Quinn).

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