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The word "unification" is borrowed from mathematical logic, where it names the process of finding a substitution that makes two expressions identical. That definition is precise and complete. The engineer who internalises it — rather than reaching for the comf...

Every inference engine requires a foundation of facts it treats as unconditionally true. In Prolog, this foundation is the Knowledge Base (KB): the complete set of facts and rules loaded into the WAM at any given moment. The correctness of every derivation the...

Prolog's execution model is not a function call graph. It is a search. Every query the engine receives is a problem statement — "find all substitutions for these variables that make this formula true" — and the engine's job is to explore the space of possible ...

An imperative loop is a mutable index advancing through a mutable array under a termination condition checked at runtime. It has three moving parts — the counter, the array pointer, and the termination predicate — all of which can be wrong independently. It al...

Every administrative command issued against production infrastructure carries an implicit precondition: the system is in the state the operator believes it to be in. zpool replace requires the failing disk to be in the specified pool. qm clone requires the sou...

Backtracking is Prolog's correctness mechanism: it exhausts all proof paths, guaranteeing that every solution is found. For general logic programming this is a virtue. For infrastructure control predicates — where a predicate must produce exactly one answer, w...

Every infrastructure record is a named collection of typed fields: a host has a name, a MAC address, a RAM capacity, a storage layout, a cluster role. In the KB architecture of Chapters 1–7, these fields are encoded as positional arguments in compound terms: p...

Prolog has one data type: the term. Rules, facts, queries, and data values are all terms. A clause physical_host('pve-node-01', 'AA:BB:CC:DD:EE:01', 256) is a term with functor physical_host and arity 3. A rule can_migrate(VM, Host) :- ... is a term with funct...