g window(Figure 15). Click
on the variable "Place" to highlight the variable with green underline,
in the mean time any associated variables (with same sort) will be highlighted
with red underline (not in this case). Right click on the green underlined
variable, a popup list will appear with two options: "home" and "office".
Instantiate the variable by selecting "home" from the popup list. Be noticed
that right click on a predicate (rather than any green underlined variables)
will allow user to delete the p