?- consult('purple_i.pl').
true.

?- digit(D,[one,two,three],Rest).
D = 1,
Rest = [two, three] .

?- digit(D,[1,2,3],Rest).
false.

?- ordinal(O,[third,fourth,fifth,sixth],Rest).
O = 3,
Rest = [fourth, fifth, sixth] .

?- sequence(S,[natural,numbers,.],Rest).
S = natural,
Rest = [numbers, '.'] .

?- operation(Value,[three,times,two],rest).
false.

?- operation(Value,[three,times,two],Rest).
Value = 6,
Rest = [] .

?- interpreter.
|: what is two plus two?
4
|: what is eleven div by four?
Error...
|: what is nine divided by four?
2.25
|: what is three minus seven?
-4
|: what is the factorial of seven?
5040
|: what is the square root of nine?
3.0
|: what is five to the third power?
125
|: display the first prime number.
2
|: display the first 5 prime numbers.
Error...
|: display the first nine prime numbers.
2 3 5 7 11 13 17 19 23
|: display the first seven factorial numbers.
Error...
|: display the first seven fibonacci numbers.
0 1 1 2 3 5 8
|: display the first six triangular numbers.
0 1 3 6 10 15
|: display the first nine natural numbers.
1 2 3 4 5 6 7 8 9
|: stop.
% Execution Aborted
?- halt.