![Figure 2](slices1.png)
Figure 2: Illustration of two hypersurfaces of a foliation
. Lapse
and shift
are defined
by the relation of the timelike unit normal field
and the basis vector
associated with the
coordinate
. Note that
and, hence, the shift vector
is tangent to
.
![Σt](article460x.gif)
![α](article461x.gif)
![βμ](article462x.gif)
![μ n](article463x.gif)
![∂t](article464x.gif)
![t](article465x.gif)
![⟨dt,αn ⟩ = 1](article466x.gif)
![β](article467x.gif)
![Σt](article468x.gif)