<\body> The standard ``fold'', ``unroll'' and ``switch'' tags implement the most frequent kinds of traversal of a slideshow. However, there are cases in which more complex successions are needed. <\big-figure|||| <\compact> Elimination of from <\equation*> x*sin y-3*x*y=\ yields <\equation*> x=|sin y-3*y>. >>>>||| <\compact> Elimination of > from <\equation*> *sin y-3**y=\ yields <\equation*> =|sin y-3*y>. >>>>> Example of highlighting a variable when switching from one slide to a next one. For instance, imagine that we are given a slide, and that we wish to highlight all occurrences of some variable in red on the next slide (see figure). This could be achieved by using a switch tag: we just copy the whole slide both in the first and in the second branch of the switch, and next color all instances of red in the second branch. However, this solution has the disadvantage that any modification on the slide has to be made both in the first and in the second branch. provides a so called ``overlay'' mechanism for this kind of more complex successions of slides. You may insert a pile of overlays using . At the start, the pile contains a unique overlay, but new overlays can then be added using the standard keyboard shortcuts and for . When applied to overlays, the standard keys and for traversing the presentation have the effect of going up and down in the pile of overlays. By default, all text which is typed by the user will be visible on all overlays. But, using the filters in the menu , it is also possible to create text which is only visible on specified overlays of the pile. There are four basic types of filters: <\description> >Text that will be visible on this and all subsequent overlays. >Text that will be visible on this and all previous overlays. >Text that will be visible only on this overlay. >Text that will be visible on all but the current overlays. <\initial> <\collection>