# File lib/BinaryConstraint.rb, line 13
        def initialize(lhs, rhs, relation)
            if relation.arity != 2
                raise ArgumentError, "The relation given must take two arguments!"
            end
            @lhs = lhs
            @rhs = rhs
            @relation = relation
        end

# File lib/BinaryConstraint.rb, line 49
        def ==(constraint)
            return false unless constraint.kind_of?(BinaryConstraint)
            (@lhs == constraint.lhs) and (@rhs == constraint.rhs) and (@relation == constraint.relation)
        end

# File lib/BinaryConstraint.rb, line 33
        def allAssigned?
            @lhs.assigned? and @rhs.assigned?
        end

# File lib/BinaryConstraint.rb, line 54
        def each
            [ @lhs, @rhs ].each { |variable|
                yield variable
            }
        end

# File lib/BinaryConstraint.rb, line 24
        def holds?
            if allAssigned?
                @relation.call(@lhs.value, @rhs.value)
            else
                raise RuntimeError, "Cannot check whether " + self.to_s +
                    " holds because not all variables have been assigned values!"
            end
        end

# File lib/BinaryConstraint.rb, line 37
        def include?(variable)
            (@lhs == variable) or (@rhs == variable)
        end

# File lib/BinaryConstraint.rb, line 60
        def revise
            # TODO: check bounds consistency rather than everything explicitly
            checks = 0
            revisedVariables = Array.new
            pruneList = Set.new
            assigned = [ @lhs, @rhs ].find { |var| var.assigned? }
            if assigned.nil?
                pruneList = @lhs.values.clone
                pruneListRight = @rhs.values.clone
                @lhs.domain.each { |lvalue|
                    @lhs.value = lvalue
                    @rhs.domain.each { |rvalue|
                        @rhs.value = rvalue
                        checks += 1
                        if self.holds?
                            pruneList.delete(lvalue)
                            pruneListRight.delete(rvalue)
                        end
                    }
                    @rhs.reset
                }
                @lhs.reset
                unless pruneList.empty?
                    @lhs.domain.prune(pruneList)
                    revisedVariables << @lhs
                end
                unless pruneListRight.empty?
                    @rhs.domain.prune(pruneListRight)
                    revisedVariables << @rhs
                end
            else
                unassigned = ([ @lhs, @rhs ] - [ assigned ]).first
                unassigned.domain.each { |value|
                    unassigned.value = value
                    checks += 1
                    pruneList << value unless self.holds?
                }
                unassigned.reset
                unless pruneList.empty?
                    unassigned.domain.prune(pruneList)
                    revisedVariables << unassigned
                end
            end
            return revisedVariables, checks
        end

# File lib/BinaryConstraint.rb, line 41
        def to_s
            @lhs.name + " " + @relation.to_s + " " + @rhs.name
        end

# File lib/BinaryConstraint.rb, line 45
        def to_s_full
            @lhs.to_s + " " + @relation.to_s + " " + @rhs.to_s
        end