\unfill

Description 

\unfill is the dual operator of \fill previously described. It is used to unfill a previously filled area. Parameters are symbol name of vertices defining the area to be cleared. Vertices can be given without any particular order. If no vertex is given the result is to unfill all faces previously filled.
This operator should only appear within a step block.

Usage

  \unfill(a, c, b, d);  % clear the previous filled square
  \unfill(a, b, d);   
  \unfill;              % clear all !

Formal structure

  \unfill;
  \unfill(VERTICES_LIST);

Parameters

  VERTICES_LIST  : Vertices used to define filled area to clear.
  Type           : List of vertex symbols.
  Allowed values : Any sequence of vertex identifiers already 
                   defined in previous steps.