Real Systems

Access Control Lists — UNIX file permissions are AND/OR/NOT over user, group, and other permission bits. chmod 755 sets specific bits; ls -l reads them back as boolean flags. The execute bit for a directory means “can traverse” — a compound access decision ANDs the traverse bit with the parent directory’s bits recursively.

Kubernetes Pod Scheduling — a Pod’s scheduling constraints are boolean expressions. nodeAffinity expressions use AND/OR to combine requirements. A node must match all required terms (AND) and any of the preferred terms (OR). The scheduler evaluates these expressions for every candidate node. An incorrectly specified affinity expression causes Pods to be scheduled to wrong nodes or not scheduled at all.

Firewall Rules — iptables and cloud security groups evaluate packets against chains of rules, each of which is a conjunction (AND) of match criteria: source IP AND destination port AND protocol. The rule matches only when all criteria match. De Morgan’s appears when rules are negated: “block all traffic except from 10.0.0.0/8” is implemented as two rules because negation distributes differently over sets of criteria.

Circuit Breakers — a circuit breaker opens (stops traffic) when failure_rate > threshold AND window_is_active. It resets (allows traffic) when probe_succeeds OR reset_timeout_expired. These are literal boolean expressions evaluated by the circuit breaker at each request. Short-circuit evaluation applies: if failure_rate > threshold is False, window_is_active may not be checked.

SQL WHERE Clauses — every SQL WHERE clause is a boolean expression over column predicates. The query optimizer applies De Morgan’s Laws and boolean identities to rewrite the expression into a form that can use indexes efficiently. WHERE NOT (a = 1 AND b = 2) may be rewritten as WHERE a != 1 OR b != 2 if that form better exploits available indexes. The optimizer is an automated De Morgan’s transformer.