April 2000
CO230 : COGNITIVE SCIENCE

QUESTION 2

Total Marks: 15 Marks

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SUGGESTED SOLUTIONS
for Question 2

(a)If it is known that
   students = {john, mary}
   subjects = {co230, ca208}
and
.   X:students pass(X,co230)
then we can deduce the following additional fact
    pass(john,co230)  pass(mary,co230)
(i)For each of the following statements,state what additional facts ay be deduced:
•~X:students pass(X,ca208)[1mark ]
X:students Y:subjects pass(X,Y) [1mark ]
X:students Y:subjects pass(X,Y) [1mark ]
•~X:subjects pass(john,X) [1mark ]
(ii)Restate the following facts as quantified predicate expressions.
•~pass(john,ca208) .~pass(john,co230) [1mark ]
•[pass(john,ca208) pass(john,co230)] v[pass(mary,ca208) pass(mary, co230)] [1mark ]
•pass(john,ca208) v pass(mary,ca208) [1mark ]


(b)Use the following predicates to answer this part of the question.
     taught_by(X,Y)          X is taughtbyY
     teach_subject(X,Y)    X teaches the subject Y
     pass(X,Y)                 X passes the subject Y
(i)Restate the following expression as an English sentence:
X Y [taught_by(X, mark) teach_subject(mark,Y)] =>pass(X, Y)
[2marks ]
(ii)Given that a student Karyn failed WW221,explain in English what can be
concluded.You should use the given expression
X Y [taught_by(X, mark) teach_subject(mark,Y)] => pass(X, Y)
and show clearly all your working and the logical rules used.[4 arks ]
(iii)Given
X Y [taught_by(X, mark) .teach_subject(mark,Y)] =>pass(X, Y)
and the knowledge that Joe passed WW221,explain if we can confidently conclude that Mark teaches WW221 and that Joe was taught by Mark.[2 marks ]