Suppose that prolog facts are used to define the predicates mother(m, y) and father(f, x), which represent that m is the mother of y and f is the father of x, respectively. Give a prolog rule to define the predicate grandfather(x, y), which represents that x is the grandfather of y. Use a comma to denote "and" and a semicolon to denote "or. ".

To the north of ginnungagap it was bitterly cold. (20) nothing was there but fields of snow and mountains made of ice. to the south of ginnungagap was a region where frost and snow were never seen. it was always bright, and was the home of light and heat. the sunshine from the south melted the ice mountains of the north so that they toppled over and fell into ginnungagap. there may be a mistake in the way the sentence is written. if you find a mistake, choose the answer that corrects the mistake. if there is no mistake, choose ‘correct as is.' a) correct as is. b) nothing was there but snow fields and mountains of ice. c) nothing was there but fields of snow and icey mountains. d) nothing was there but fields of snow and mountains of ice.