Add green cuts to the following program

class(Number,positive)  :-  Number  >  0. 
class(0     ,zero    ). 
class(Number,negative)  :-  Number  <  0.

Such that we immediately get the correct result.

Not like this:

?- class(5,positive).
true ;
false.

But like this:

?- class(5,positive).
true.