Editing Method of analytic tableaux (section)

===Auxiliary tableaux===

A different method for dealing with formulae holding in alternate worlds is to start a different tableau for each new world that is introduced in the tableau. For example, <math>\neg \Box A</math> implies that <math>A</math> is false in an accessible world, so one starts a new tableau rooted by <math>\neg A</math>. This new tableau is attached to the node of the original tableau where the expansion rule has been applied; a closure of this tableau immediately generates a closure of all branches where that node is, regardless of whether the same node is associated other auxiliary tableaux. The expansion rules for the auxiliary tableaux are the same as for the original one; therefore, an auxiliary tableau can have in turns other (sub-)auxiliary tableaux.