/** ***************************************************************************************************************************
*this is only applicable using the database that Jamie has used during his lecture. in this case its lecture 17 [l17] database*
*************************************************************************************************************************** **/

bad(x) :- bad(x). 
/** this is prolog version of "fun f x = f x" in ML **/
/** these loops are very easy to generate **/

heads(win, jamie).
/** returns false, lecture video (pretty early, about 9min in.) **/

tails(win, jamie).
/** returns an error of "out of local stack", as there are subgoals for "tails" call in the database **/

/** ***************************************************************************************************************************
*                                                database manipulations                                                       *
*************************************************************************************************************************** **/

film(good, high-anxiety).
/** returns an error of "undefined procedure" **/

asserta(film(good, high-anxiety)).
/** inserts a entry in the database of "film(good, high-anxiety)." **/

asserta(film(good, terminator)).
/** inserts an entry for "film(good, terminator)." **/
/** "asserta" adds entries to the begining of the database **/
/** entries are added to the dynamic database. **/

asserta(plays(charles)).
/** insters an entry for "plays(charles)." **/
/** would return an error as dynamic database is unable to predicates that already exist in the static database **/
/** dynamic and static databases are completely separe **/

film(bad, prometheus).
/** once the static database has an entry with the same predicate as an entry in dynamic database, all entries with that predicate are wiped form dynamic database **/

assertz(bad, terminator).
/** adds entry to the end of the database **/
/** entries can only be added to either begining or end of the database **/
/** once prolog is closed both the dynamic and static databases are removed from memory **/

retract(film(bad, terminator)).
/** removes the entry for "film(bad, terminator)." **/

retract(film(X, Y)).
/** it matches and deletes clauses it finds, unless "enter" or "y" is pressed. **/

abolish(film/2).
/** abolishes all predicates which require 2 arrities for the named predicate **/
/** removes the information about the predicate as well **/

retractall(film(X, Y)).
/** removes all entries withtout inquiring of the user/programmer **/
/** keeps the information about the predicate, but removes the entries **/

retractall(X).
/** removes all entries, but provides a warning "did not clear exception" **/

check_invitations(N).
/** returns an initial of "N=3" instanciation **/
/** imperative and function languagess **/