© 2000 Todd Neller.  A.I.M.A. text figures © 1995 Prentice Hall.  Used by permission.
Consistency enforcement
•In the simplest case, we try to instantiate a variable with each value in its domain.
•What of unary constraints? 
–e.g. “Vermont must be colored green.”, “Massachusetts must be blue or green.”
•Much search can be wasted if such simple constraints are ignored.