; Metalinguistic Abstraction II with Hal
; Implementing a declarative/logical programming language.

; How does the pattern-matcher work?
; => 8B:(4m32s) What is a primitive QUERY?
; Implementing the Means of Combination.
; => 8B:(16m55s) Coming back to the concept of CLOSURE.
; interesting QUESTIONS 8B:(17m5s) => 8B:(22m9s) BREAK

; Implementing the Means of Abstraction.
; 8B:(27m31s) => We need a more general pattern-matcher
;                which is called a UNIFIER.
; 8B:(30m26s) => The hard cases, where fixed-point equations
;                must be solved... are skipped.

;;; FORMAL DEFINITION
; To Apply a Rule
;  Evaluate the rule body relative to an environment formed
;  by unifying the rule conclusion with the given query.
; To Apply a Procedure
;  Evaluate the procedure body relative to an environment
;  formed by binding the procedure parameters to the arguments.

; 8B:(36m18s) A tiny technical problem: variable-conflicts
;   => need for local variables.
; Fundamental QUESTIONS 8B:(38m21s) => 8B:(47m50s) BREAK

; Logic programming is NOT the same as logic.
; Classical logic:
;   ALL HUMANS ARE MORTAL.
;   ALL GREEKS ARE HUMAN.
;   SOCRATES IS A GREEK.
;   . . .
;   SOCRATES IS MORTAL.
; Logic Database:
;   (Greek Socrates) (Greek Plato)
;   (Greek Zeus)     mo Zeus)
;
;   (rule (mortal ?x) (human ?x))
;   (rule (fallible ?x) (human ?x))
;
;   (rule (human ?x)
;      (and (Greek ?x) (not mo ?x))))
;   (rule (address ?x Olympus)
;      (and (Greek ?x) mo ?x)))
;   (rule (perfect ?x)
;      (and (not (mortal ?x))
;           (not (fallible ?x))))
;
;   (and (address ?x ?y)
;        (perfect ?x))
;   => OLYMPUS
;   (and (perfect ?x)
;        (address ?x ?y))
;   => [NOTHING]
; "Not is not NOT (in the logical sense)." --Hal
; 8B:(58m27s) How to fix the wrong answer?
; ...WAIT
; 8B:(58m50s) "Which of these is the right answer?" --Hal
; How did the system deduce OLYMPUS?
; There are no clues that Zeus is not mortal or fallible.

; 8B:(1h3m58s) "How do you bridge the gap from this world
;               of logic and relations to the worlds of more
;               traditional languages and somehow combine
;               the power of both?" --Hal
; important QUESTIONS (END)