1. ## logicsets 3

can anyone do this question, im really stuck:

Alan, Barbara, Charles ara chooses Colin Dexter
and Jane Austen, Charles chooses dicck Francis, Colin Dexter and Terry Pratchett, and Deborah chooses Jane Austen and Terry Pratchett.

(a) Denoting the shere l, d, a, f and p stand for Robert Ludlum, Colin
Dexter, Jan
above.

(b) Explain w between people and authors.

(c) Use projection and inverse projectiochosen by Barbara.

(d) Use projectssion for all the readers choosing both dicck
Francis and Robert Ludlum.

thank you

2. Originally Posted by srk619
can anyone do this question, im really stuck:

Alan, Barbara, Charles and Deborah each have to pick two authors they read.
Alan chooses Robert Ludlum and Colin Dexter, Barbara chooses Colin Dexter
and Jane Austen, Charles chooses dicck Francis, Colin Dexter and Terry Pratchett, and Deborah chooses Jane Austen and Terry Pratchett.

(a) Denoting the set of people by P = {A, B, C, D} where A, B, C and D stand
for Alan, Barbara Charles and Deborah respectively and the set of authors
by A = {L, d, a, f , p}, where l, d, a, f and p stand for Robert Ludlum, Colin
Dexter, Jane Austen, dicck Francis, and Terry Pratchett respectively, give a
relation (i.e. a subset of P x A) which encapsulates the information given
above.

(b) Explain why it is not possible to use a function from P → A or a function
from A → P to give the relationship between people and authors.

(c) Use projection and inverse projection mappings to give an expression for
the names of all the authors chosen by Barbara.

(d) Use projection and inverse projection mappings together with set algebraic
operations to given an expression for all the readers choosing both dicck
Francis and Robert Ludlum.

thank you

The relation is:

R={ (A,l),(A,d),(B,d),(B,a),(C,f),(C,d),(C,p),(D,a),(D ,p)}.

Now we cannot have a function from P to A, BECAUSE one of the conditions that must be satisfied by a function is that:

No two ordered pairs have the same 1st member.

And in our case we do have two ordered pairs with the 1st member,

[ (A,l),(A,d) ]

3. ## help

i can do the mapping but i dont know how to
set algebraic
operations to given an expression for all the readers choosing both dicck
Francis and Robert Ludlum.