# File ai/csp/int.rb, line 32
        def propagate(variable, level)
            v = @variables[@variables.index(variable) - 1]
            return true if v.instantiated?

            v.each_value_with_index(level) { |value, index|
                v.prune(level, index) unless value == variable.value
            }
            not v.domain_empty?(level)
        end