Prolog In tro duction Prolog programmi ng F acts ab out - - PDF document

SLIDE 1

• Prolog

In tro duction Prolog programmi ng

• F

acts ab

• ut
• b

jects

• Rules

ab

• ut
• b

ject relationships and prop erties

• Questions

ab

• ut
• b

jects relationships prop erties

SLIDE 2 Prolog

• F

acts Syn tax

• Names
• f

relationships and

• b

jects b egin with a lo w er case letter

• The

relationship name is giv en rst related

• b

jects are enclosed in paren thesis and separated b y commas This commaseparated list is the argu men t

• f

the relationship

• F

act sen tences end in a PERIOD

SLIDE 3 Prolog

• Seman

tics

• The

pr

• gr

ammer is resp

• nsible

for deciding up

• n

the meaning asso ciated with relationships dogspot Sp

• t

is a dog fathergerry deb Gerry is the father

• f

Deb petspot cindy Sp

• t

is the p et

• f

Cindy playjohn mary tennis John and Mary pla y tennis

• Ob

jects spot cindy gerry deb

• Relationships

dog father pet

SLIDE 4 Prolog

• This

means there migh t b e am biguities in the in terpretation

• f

program results Do es

• ldergerry

brian mean

• gerry

is

• lder

than brian

• r
• brian

is

• lder

than gerry By con v en tion w e usually write relationship descriptions lik e this relationshipobj

• bj

means

• bj

is relationship tooffor

• bj

SLIDE 5 Prolog

• Questions

W e can ask questions ab

• ut

facts Supp

• se

w e had the database giv en ab

• v

e dogspot This is the question yes This is the answer Answ ers ma y

• nly

use facts in the database

• r

facts that ma y b e deduced from the database Th us dogmeg no No fact de claring me g to b e a do g NO means Pr

• lo

g c annot de duc e an answer not false W e can use v ariables These are indicated b y an upp er case letter W e can ha v e sev eral v ariables playXYZ X

• john

Y

• mary

Z

• tennis

Prolog lo

• ks

through the database and determines whether there is a set

• f

assignmen ts to X Y Z that will mak e playX Y Z true Sometimes there will b e more than

• ne

p

• ssible

list Supp

• se

w e ha v e the follo wing facts playjohn mary tennis playjohn mary baseball playjohn bill basketball Ask the same question playXYZ X

• john

Y

• mary

Z

• tennis
• X
• john

Y

• mary

Z

• baseball
• X
• john

SLIDE 6 Prolog

• Y
• bill

Z

• basketball
• no

There w ere three sets

• f

assignmen ts to X Y Z that w

• uld

mak e the ques tion true Prolog con tin ues returning these v ariable assignmen ts un til no more remain W e can restrict

• ur

queries asking who pla ys tennis playXYtennis

• X
• john

Y

• mary

When Prolog matc hes an

• b

ject with a v ariable w e sa y that the v ariable has b een instantiate d to that v alue

• Conjunctions

W e can construct more complicated questions b y using conjunctions Supp

• se

w e use a new database playjohn mary tennis playjohn mary baseball playjohn bill basketball playbill mary tennis playbill mary basketball W e w

• uld

lik e to kno w who pla ys John b

• th

in tennis and in bask etball playjohnYten nis playjohn Y basketball

• Y
• bill

Prolog will

• nly

return instan tiations for Y that will mak e mak e b

• th

parts

• f

the question the goals true at

• nce
• Rules

Rules are a con v enien t w a y to state something ab

• ut

a collection

• f
• b

jects W e can alw a ys list eac h fact separately for ev ery

• b

ject horserobin horsemac horsesecretari at

SLIDE 7 Prolog

• dogmeg

dogspot doglassie animalrobin animalmeg animalsecretar iat animalmac animallassie animalspot likesdebrobin

• likesdebmeg

likesdebsecre taria t likesdebmac likesdeblassi e likesdebspot

• Ho

w ev er this gets unreasonably length y

• By

adding rules ab

• ut

relationships b et w een

• b

jects w e can signican tly cut do wn

• n

the database size horserobin horsemac horsesecretari at dogmeg dogspot doglassie animalX

• horseX

animalX

• dogX

likesdebX

• animalX

The last three statemen ts are rules In English w e w

• uld

sa y

• animalX
• horseX

If there is some X that is a horse then that X is an animal

• likesdebX
• animalX

If there is some X that is a horse then that deb lik es that X Prolog do esnt care ab

• ut

the truth

• f

the rules they are statemen ts b y the programmer This rule sa ys that all studen ts lik e studying

SLIDE 8 Prolog

• likesXstudyin

g

• studentX
• Rules

are also useful for making denitions featherstweety

• yellowtweety

animaltweety furmeg whitemeg animalmeg barksmeg furrobin paintrobin animalrobin neighsrobin birdX

• feathersX

animalX

• dogX
• furX

barksX animalX

• horseX
• furX

neighsX animalX

• W

ev e dened

• A

bird as an animal with feathers

• A

dog as an animal with fur that barks

• A

horse as an animal with fur that neighs W e can ask questions furX X

• meg
• X
• robin

dogX X

• meg

Rule dep endencies can in tro duce new conditions Notice that M F app ear

• nly
• n

the righ t hand side

• f

the rule

• Family
• f

Queen Victoria

• malealbert

maleedward femalealice

SLIDE 9 Prolog

• femalevictoria
• Albert

and Victoria are the parents

• f

Edward

• parentsedward

victoria albert parentsalice victoria albert

• X

is the sister

• f

Y if

• sisterOfX

Y

• femaleX
• X

is female

• parentsX

M F

• parents

are the same

• parentsY

M F

• parents

are the same

• X

is the brother

• f

Y if

• brotherOfX

Y

• maleX
• X

is male

• parentsX

M F

• parents

are the same

• parentsY

M F

• parents

are the same

• W

e can use Prolog rules to calculate things

• Population

in millions

• f

people in

• popX

Y

• The

population

• f

X is Y million people

• popusa

popindia popchina popbrazil

• Area

in millions

• f

square miles in

• areaX

Y

• The

area

• f

X is Y million square miles

• areausa

areaindia areachina areabrazil

• Density

is population divided by area

• densityX

Y

• The

density

• f

X is Y people per square mile

• densityX

Y

• popX

P

• population
• f

X is P

• areaX

A

• area
• f

X is A

• Y

is PA

• density

Y is population P

• ver

area A

• W

e can ask questions ab

• ut

densit y no w

SLIDE 10 Prolog

• densityusaY

Y

• densitychinaY
• Y
• densityCountry
• Country
• india

T races for the rst t w

• queries

using BinProlog

• consultpopulatio

n consultingpopu latio n consultedpopul ation time

• yes
• tracedensitychi

naY

• Call

densitychina

• dynamicdensity

Call popchina

• dynamicpop

Exit popchina Call areachina

• dynamicarea

Exit areachina Call

• is
• compiledis

Exit

• is
• Exit

densitychina

• Y

Redo densitychina

• Redo
• is
• Fail
• is
• Redo

areachina Fail areachina Redo popchina Fail popchina Fail densitychina

• no

Note that not all Prolog in terpreters will come up with the same answ ers for the ab

• v

e Op enProlog is able to determine that

• is

equiv alen t to

• but

BinProlog do es not

• tracedensityCou

ntry

SLIDE 11 Prolog

• Call

density

• dynamicdensity

Call pop

• dynamicpop

Exit popusa Call areausa

• dynamicarea

Exit areausa Call

• is
• compiledis

Fail

• is
• Redo

areausa Fail areausa Redo popusa Exit popindia Call areaindia

• dynamicarea

Exit areaindia Call

• is
• compiledis

Fail

• is
• Redo

areaindia Fail areaindia Redo popindia Ho w ev er if y

• u

rephrase the question so that densit y is giv en as a real n um b er BinProlog also succeeds

• densityCountry
• Countryindia

no

• tracedensityCou

ntry

• Call

density

• dynamicdensity

Call pop

• dynamicpop

Exit popusa Call areausa

• dynamicarea

Exit areausa Call

• is
• compiledis

Fail

• is

SLIDE 12 Prolog

• Redo

areausa Fail areausa Redo popusa Exit popindia Call areaindia

• dynamicarea

Exit areaindia Call

• is
• compiledis

Exit

• is
• Exit

densityindia

• Countryindia

Redo densityindia

• W

e can also use comparators lik e

• in
• ur

rules

• Who

reigned in Wales th and th Centuries

• reignsrhodri
• reignsanarawd
• reignshywelDda
• reignsIago
• reignshwelApI
• reignscadwallo

n

• reignsmaredudd
• princeX

Y X was a prince in year Y if X reigned between years A B and year Y is between A B inclusive

• princeX

Y

• reignsX

A B

• X

reigned and

• Y
• A
• target

year is

• n
• r

after start

• f

reign

• Y
• B
• target

year is before

• r

equal end

• f

reign

• Some

questions princecadwallo n

• yes

SLIDE 13 Prolog

• princerhodri
• no

princeX

• X
• cadwallon
• X
• maredudd
• Matc

hing rules

• An

uninstan tiated v ariable matc hes an y

• b

ject

• Once

a v ariable has b een matc hed it is instan tiated to ha v e the v alue

• f

the

• b

ject

• In

tegers and atoms

• nly

matc h themselv es

• Structures

matc h

• ther

structures if the functor name and n um b er

• f

ar gumen ts matc h and instan tiated v ariables

• r

explicitly named argumen ts matc h

• Data

Structures

• Represen

tation W e sometimes think

• f

Prolog clauses as trees in b y in Figprologtree scaled

• This

is esp ecially handy in describing more complicated clauses suc h as this

• ne

sentencenounX

• verbphraseverb

Y nounZ in b y in Figprologsen tence scaled

• W

e can mo dify

• ur

tree to include cycles it is a graph no w when w e w an t to indicate sharing in b y in Figsharing scaled

• Lists

Characteristics

• f

Prolog lists

• Ordered

sequence

• f
• b

jects

• Commaseparated
• An

y length

SLIDE 14 Prolog

• Ma

y b e nested

• Ma

y include an y t yp e

• f
• b

ject Examples

• the

empty list

• we

the people

• element

list

• we

the people

• f

the united states

• element

list

• As

with Lisp lists ha v e a head and a tail List Head T ail abc a bc we the people we the people we the people we the people W e can use patterns to indicate the head and tail

• f

lists

• head
• rest
• and

w e can use placeholders to

• is

sometimes called the anon ymous v ariable

• X

Consider the follo wing mylistthis is a list containing some words

• queries
• mylistX

X

• thisisalist

cont ainin gso mewo rds mylistHeadTa il Head

• this

Tail

• isalistcontai

ning some word s

• One

placeholder

• mylistY

Y

• isalistcont

ainin gsom ewo rds

• two

placeholders

• mylistY
• Y
• alistcontain

ings

• mew
• rds

SLIDE 15 Prolog

• three

placeholders

• mylistY
• Y
• listcontainin

gsom ewor ds

• four

placeholders

• mylist

Y Y

• containingsom

ewor ds

• nested
• mylist

Y

• Y
• somewords

mylistXYZ

• X
• this

Y

• is

Z

• alistcontain

ings

• mew
• rds
• Lets

build something useful member Rules

• X

will b e a mem b er

• f

Y if X is the head

• f

Y memberXX W e could also ha v e written this rule memberXY

• X
• Y
• X

will b e a mem b er

• f

Y if X is in the tail

• f

Y memberX Y

• memberX

Y What ab

• ut

this memberaabc

• yes

memberaX X

• a
• is

a unique iden tier Prolog uses to indicate an un b

• und

v ariable in the answ er Things to w atc h

• ut

for

• Mutually

recursiv e rules

SLIDE 16 Prolog

• parentA

B

• childB

A childA B

• parentB

A

• Ordering
• Prolog

alw a ys starts at the top

• f

the rule base and w

• rks

do wn so p

• rly
• rder

rule sets

• ften

w

• nt

w

• rk

memberX Y

• memberX

Y memberXX Another example

• f

list programs append

• appendX

Y Z append Y to X producing Z

• append

L L appendHead

• TailFirst

SecondList Head

• Rest
• append

TailFirst SecondList Rest

• Some

queries appendabc xy z Result Result

• abcxyz

appendX Y abc X

• Y
• abc
• X
• a

Y

• bc
• X
• ab

Y

• c
• X
• abc

Y

• no

T racing the rst query

• traceappendab

c xyz Re sult

• Call

appendabcxy z

• dynamicappend

Call appendbcxy z

• dynamicappend

SLIDE 17 Prolog

• Call

appendcxyz

• dynamicappend

Call appendxyz

• dynamicappend

Exit appendxyz x yz

• Exit

appendcxyz c xy z Exit appendbcxy zb cx yz

• Exit

appendabcxy z ab cxy z Resultabc xyz

• Redo

appendabcxy z ab cxy z Redo appendbcxy zb cx yz

• Redo

appendcxyz c xy z Redo appendxyz x yz

• Fail

appendxyz

• Fail

appendcxyz

• Fail

appendbcxy z

• Fail

appendabcxy z

• no

T racing the last query is ev en more in teresting

• traceappendX

Y abc Call append ab c

• dynamicappend

Exit appendabc abc

• X

Yabc Redo appendabc abc

• Call

append bc

• dynamicappend

Exit appendbcb c Exit appendabca bc

• Xa

Ybc Redo appendabca bc

• Redo

appendbcb c Call append c

• dynamicappend

Exit appendcc

• Exit

appendbcb c Exit appendabca bc

• Xab

SLIDE 18 Prolog

• Yc

Redo appendabca bc

• Redo

appendbcb c Redo appendcc

• Call

append

• dynamicappend

Exit append Exit appendcc

• Exit

appendbcb c Exit appendabc abc

• Xabc

Y Redo appendabc abc

• Redo

appendbcb c Redo appendcc

• Redo

append Fail append

• Fail

append c

• Fail

append bc

• Fail

append ab c no

• Accum

ulators Sometimes w e need to carry temp

• rary

v alues along during a deriv ation listlenListLe ngth

• lengthAccList
• Length
• lengthAcc

A A lengthAccHead Tail

• Acc

Len

• Acc

is Acc

• add
• for

the head

• lengthAcc

Tail Acc Len

• count

the tail

• listlenabc

dLe ngth

• Length
• In

this example w e ha v e a helping clause that do es the w

• rk

and listlen initializes it Notice that lengthAcc creates a temp

• rary

v ariable Acc whic h app ears

• nly
• n

the righ t hand side Subgoal list for lengthAcc

SLIDE 19 Prolog

• lengthAccab

cd

• Len

lengthAccbc d Len lengthAcccd

• Len

lengthAccd

• Len

lengthAcc Len

• done
• Or

lo

• king

at the actual trace

• tracelistlena

bcd Len gth

• Call

listlenabcd

• dynamiclistlen

Call lengthAccabcd

• dynamiclengthAcc
• Call
• is
• compiledis

Exit

• is
• Call

lengthAccbcd

• dynamiclengthAcc
• Call
• is
• compiledis

Exit

• is
• Call

lengthAcccd

• dynamiclengthAcc
• Call
• is
• compiledis

Exit

• is
• Call

lengthAccd

• dynamiclengthAc

c Call

• is
• compiledis

Exit

• is
• Call

lengthAcc

• dynamiclengthAcc

Exit lengthAcc Exit lengthAccd Exit lengthAcccd

• Exit

lengthAccbcd

• Exit

lengthAccabcd

• Exit

listlenabcd

• Length

Another useful accum ulator

• Defining

what an integer is

SLIDE 20 Prolog

• isinteger

isintegerX

• isintegerY

X is Y isinteger yes isinteger yes isintegerX X

• X
• X
• The

Cut Sometimes w e dont w an t to pro duce list

• f

instan tiations but

• nly

a single

• ne

W e can use the cut sym b

• l
• to

indicate this divideN N Result

• isintegerResul

t

• prolog

built in

• Product

is ResultN Product is Result

• N

Product

• N

Product

• N
• Query
• divideRes

ult Result

• Lets

trace the result

• tracedivide

Resu lt Call divide

• dynamicdivide

Call isinteger

• dynamicisinteger
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Call
• is
• compiledis

SLIDE 21 Prolog

• Exit
• is
• Call
• compiled

Exit

• Call
• compiled

Fail

• Redo
• Fail
• Redo
• is
• Fail
• is
• Redo
• is
• Fail
• is
• Redo

isinteger Call isinteger

• dynamicisinteger
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Call
• is
• compiledis

Exit

• is
• Call
• compiled

Exit

• Call
• compiled

Fail

• Redo
• Fail
• Redo
• is
• Fail
• is
• Redo
• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Call isinteger

SLIDE 22 Prolog

• dynamicisintege

r Exit isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Call
• is
• compiledis

Exit

• is
• Call
• compiled

Exit

• Call
• compiled

Fail

• Redo
• Fail
• Redo
• is
• Fail
• is
• Redo
• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Call isinteger

• dynamicisinteg

er Exit isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

SLIDE 23 Prolog

• Exit
• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Call
• is
• compiledis

Exit

• is
• Call
• compiled

Exit

• Call
• compiled

Fail

• Redo
• Fail
• Redo
• is
• Fail
• is
• Redo
• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Call isinteger

• dynamicisinteger
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is

SLIDE 24 Prolog

• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Call
• is
• compiledis

Exit

• is
• Call
• compiled

Exit

• Call
• compiled

Exit

• CUT

Exit divide Result Redo divide Fail divide no What happ ens if w e dont use the cut W ed k eep generating in tegers though none

• f

the

• thers

w

• uld

ev er pass the test Heres part

• f

the trace

• successful

computation

• f
• Result
• now

try for another solution

• Redo

divide Redo

• Fail
• Redo
• Fail
• Redo
• is
• Fail
• is
• Redo
• is

SLIDE 25 Prolog

• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Call isinteger

• dynamicisinteger
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Call
• is
• compiledis

Exit

• is
• Call

SLIDE 26 Prolog

• compiled

Fail

• Redo
• is
• Fail
• is
• Redo
• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Call isinteger

• dynamicisinteger
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is

SLIDE 27 Prolog

• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Call
• is
• compiledis

Exit

• is
• Call
• compiled

Fail

• Redo
• is
• Fail
• is
• Redo
• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Call isinteger

• dynamicisintege

r Exit isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger

SLIDE 28 Prolog

• Call
• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Call
• is
• compiledis

Exit

• is
• Call
• compiled

Fail

• Redo
• is
• Fail
• is
• Redo
• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger

SLIDE 29 Prolog

• Redo
• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Call isinteger

• dynamicisinteg

er

• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

SLIDE 30 Prolog

• Exit
• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Call
• is
• compiledis

Exit

• is
• Call
• compiled

Fail

• Redo
• is
• Fail
• is
• Redo
• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger Redo

• is
• Fail
• is
• Redo

isinteger

SLIDE 31 Prolog

• Call

isinteger

• dynamicisinteger
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Exit

isinteger Call

• is
• compiledis

Exit

• is
• Call
• is
• compiledis

SLIDE 32 Prolog

• Exit
• is
• Call
• compiled

Fail

• Redo
• is
• Fail
• is
• Redo
• is
• Fail
• is
• Redo

isinteger

• Break

by sending CTRLC

• Sometimes

the cut can cause problems

• we ve

asked for A B such that AB

• divideAB
• OpenProlog
• unclassifiederr
• r

goal is

• BinProlog
• variableinis
• errorinis
• is
• Supp
• se

that w e mo died append to use the cut append L L

• appendHead
• TailFirst

SecondList Head

• Rest
• append

TailFirst SecondList Rest

• queries

this

• ne

works

• appendabc

def Result Result

• abcdef
• this

query no longer works

• appendX

Y abc X

• Y
• abc
• no

The cut command prev en ted Prolog from making c hanging X and Y so w e didnt get the full list

• f

solutions that w e receiv ed b efore