Prolog

Question 1

B :- A

Answer 1

Implication, A -> B

Question 2

,

Answer 2

And

Question 3

;

Answer 3

Or

Question 4

Atom

Answer 4

1. A sequence of letters, digits or underscores that starts with a lowercase letter (car)
2. A sequence of letters, digits or underscores that are enclosed in single quotes (‘car’)
3. A string of special characters (:- or ,) (without the quotes, thus not a Python string format)

Question 5

Number

Answer 5

Any sequence of numbers, possibly containing a dot

Question 6

Variable

Answer 6

A sequence of letters, digits or underscores that starts with an upper case letter or an underscore (Car)

_ is the anonymous variable

Question 7

A term is defined recursively:

Answer 7

1. Each constant and variable is a term
2. f(t1, …, tk) is a term is each ti is a term and f is an atom
   — (this is a compound term with functor f and arity k indicated as has_wheels/1)
   — a term is a ground when it contains no variables

Question 8

Predicate

Answer 8

Any constant or compound term

Question 9

Fact

Answer 9

A predicate immediately followed by a dot

Question 10

Rule

Answer 10

A predicate is a rule if:

• given by A0 :- A1, …, An. With n>=0 and each Ai a predicate.

A0 is the head, A1, …, An is the body of the rule

Question 11

Clause

Answer 11

Any fact or rule,
Are universal

Question 12

Definition of a predicate

Answer 12

The set of all facts and rules that use a certain predicate P,

if there is no definition in a certain program, P is called undefined

Question 13

Built in predicate

Answer 13

Defined by SWI Prolog (member/2)

Question 14

Query

Answer 14

Defined as ?-p
Where p is some predicate known as a goal

Question 15

Constant

Answer 15

Atoms and numbers

Question 16

Two terms t1 and t2 match iff

Answer 16

1. t1 and t2 are identical constants
2. If t1 is a variable and t2 is not, then t1 is instantiated with t2
   — the same applies for the reverse of when both are variables
3. If t1 and t2 are compound terms, they match if:
   — they have the outermost functor (t1 =(r1,…,rk) and t2=(s1,…,sk))
   — each term ri matches with each term si
   - the variables instantiations are compatible, variables can’t be assigned different terms which are not variables

Question 17

=/2

Answer 17

Matching predicate, binds variables using the most general unifier

Question 18

=/2

Answer 18

Can be used to check terms that do not match

Question 19

/+

Answer 19

Negationwith finite failure

/+ f is true in program P iff f cannot be derived from P and the program terminates

/+ G can be derived from P iff the search tree of P for G is finitely failed

Its not saying f is false, it is saying there is not enough information to prove f is true

Question 20

A search tree for a program for a goal is called finitely failed when:

Answer 20

• No successful branch in the tree
• no infinite branch

Question 21

=:=

Answer 21

Checks if computation on the left is equal to computation on the right

(4+3=:=5+2 evaluated to True)

Question 22

==

Answer 22

Checks if the computation on the left differs from the computation on the right

4+3==5+2 evaluates to false

4+3==2+2 evaluates to true

Question 23

is operator

Answer 23

Has an arithmetic expression on the right side, evaluates it and unifies the result with the variables in the left side

Left side:
- variable
- it checks if this value matches the evaluated result of the expression the right

(X is 2+2 evaluates X=4)

Question 24

Lists

Answer 24

Store compound terms

Symbol:
[] (empty list has no head or tail)

Have a head (term) and a tail (list)
Head is the first element alone, tail is the rest of the body
[Head|Tail]

Question 25

[|]/2 operator

Answer 25

Allows to concatenate terms in lists [|] (a,[]) evaluates to [a]

Question 26

Strings

Answer 26

1. Atoms: Used for identifiers and comparison, not manipulation - car(‘Ferarri’) 2. Are lists of characters - ‘hello’ -> [h,e,l,l,o] 3. List of character codes, which are used when parsing 4. String type

Question 27

String type (swi prolog)

Answer 27

- Represent text as a unit, but can be composed, decomposed or converted - indicated by double quotes

Question 28

Recursion

Answer 28

A recursive definition is defined in terms of itself A method of solving a problem where the solution depends on solutions to smaller instances of the same problem Include termination condition

Question 29

Reachable A predicate pred2 is reachable from predicate pred1 in a program P if:

Answer 29

1. There is a rule in P the head of which uses pred1 and the body which contains pred2. Or 2. There is a predicate pred3 such that pred3 is reachable from pred1 in P, and pred2 is reachable from pred3 in P pred1(X):- pred2(X) pred1(X):- pred3(X) pred3(X):- pred2(X)

Question 30

When is a predicate pred defined recursively?

Answer 30

If there is at least one rule in the definition of pred in P from which pred itself is reachable

Question 31

Left recursion

Answer 31

The base case comes after the recursive case AVOID IT

Question 32

Non termination

Answer 32

The program won’t terminate because it ends in an infinite branch

Question 33

Depth first search

Answer 33

Used by prolog, start at the root node and explore as far as possible along each branch before backtracking

Question 34

What does it mean for a goal to be derived or proven in prolog?

Answer 34

A goal G can be derived or proven from a program P if Prolog finds a successful trace in the search tree of P for G

Question 35

Declaritive meaning

Answer 35

The logical meaning of the program, ignoring prolongs specific search strategy

Question 36

Procedural meaning

Answer 36

The answer computed by prolog, considering its specific search strategy (Can differ from declarative meaning)

Question 37

Incompleteness

Answer 37

Property of prolog proof search, does not always find derivation, even if derivation exists

Question 38

Incorrectness

Answer 38

Lack of an occurs check in prolog