Order of clauses

• As mentioned previously, the reservations against cut - lose correspondence between declarative and procedural meaning of programs
• If no cut, and since program is declarative - possible to change order of clauses and goals
• This re-ordering may affect program efficiency or termination - BUT - has no influence on program correctness or declarative meaning (as the solution to a query is obtained by searching the program in a top-down manner, and answering the goals from left to right
• However, in programs with cut, a change in the order of the clauses may affect the meaning (declarative)
• We can get different results (depending on the query)

p :- a,b.
p :- c.
means p = (a and b) or c

p :- a, !, b.
p :- c.
means p = (a and b) or (~a and c)

swapping clauses

p :- c.
p :- a, !, b.
means p = c or (a and b)