A pair of zips, each zip being half a zipper, which can be zippered up to close a surface along a curve. The concept of a zip-pair can be extremely useful in topological arguments, and zips can be used to illustrate the construction of the cap, cross-cap, handle, and cross-handle.
Zip-Pair
See also
ZipExplore with Wolfram|Alpha
References
Francis, G. K. and Weeks, J. R. "Conway's ZIP Proof." Amer. Math. Monthly 106, 393-399, 1999.Referenced on Wolfram|Alpha
Zip-PairCite this as:
Weisstein, Eric W. "Zip-Pair." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Zip-Pair.html