Double a number - back to content

		Example:
		
		/* Loads the file ex1.pro:     */
		?- [ex1]. 
		yes
		?- double. 
		Please input a number?  3.
		Double is 6

You write this code in a text file called ex1.pro. nl - means new line /* Those are comments in Prolog. Always write something about your predicate. */ double:- write('Please input a number? '), read(X),nl, write('Double is '), Y is 2 * X, write(Y),nl.