def kb_retract(self, fact_or_rule):
        """Retract a fact from the KB
        Args:
            fact (Fact) - Fact to be retracted
        Returns:
            None
        """
        printv("Retracting {!r}", 0, verbose, [fact_or_rule])
        ####################################################
        # Student code goes here

        if isinstance(fact_or_rule, Fact) and fact_or_rule in self.facts:
            arg_in_kb = self.facts.index(fact_or_rule)
            if (self.facts[arg_in_kb].asserted is True and not self.facts[arg_in_kb].supported_by) or \
                    (self.facts[arg_in_kb].asserted is False and not self.facts[arg_in_kb].supported_by):
                facts_to_be_checked = self.facts[arg_in_kb].supports_facts
                rules_to_be_checked = self.facts[arg_in_kb].supports_rules
                if facts_to_be_checked:
                    for fact in facts_to_be_checked:
                        self.kb_retract_helper(fact, fact_or_rule, "f")
                if rules_to_be_checked:
                    for rule in rules_to_be_checked:
                        self.kb_retract_helper(rule, fact_or_rule, "r")
                self.facts.remove(fact_or_rule)

            elif self.facts[arg_in_kb].asserted is True and self.facts[arg_in_kb].supported_by:
                self.facts[arg_in_kb].asserted = False

        elif isinstance(fact_or_rule, Rule) and fact_or_rule in self.rules:
            arg_in_kb = self.rules.index(fact_or_rule)
            if self.rules[arg_in_kb].asserted is False and not self.rules[arg_in_kb].supported_by:
                facts_to_be_checked = self.rules[arg_in_kb].supports_facts
                rules_to_be_checked = self.rules[arg_in_kb].supports_rules
                if facts_to_be_checked:
                    for fact in facts_to_be_checked:
                        self.kb_retract_helper(fact, fact_or_rule, "f")
                if rules_to_be_checked:
                    for rule in rules_to_be_checked:
                        self.kb_retract_helper(rule, fact_or_rule, "r")
                self.rules.remove(fact_or_rule)