Editing Boy's surface (section)

==Applications==
Boy's surface can be used in [[sphere eversion]] as a [[half-way model]].  A half-way model is an immersion of the sphere with the property that a rotation interchanges inside and outside, and so can be employed to evert (turn inside-out) a sphere.  Boy's (the case p&nbsp;=&nbsp;3) and [[Morin surface|Morin's]] (the case p&nbsp;=&nbsp;2) surfaces begin a sequence of half-way models with higher symmetry first proposed by George Francis, indexed by the even integers 2p (for p odd, these immersions can be factored through a projective plane).  Kusner's parametrization yields all these.