diff_color(red,blue).
diff_color(blue,red).
diff_color(red,yellow).
diff_color(yellow,red).
diff_color(blue,yellow).
diff_color(yellow,blue).
diff_shape(circle,square).
diff_shape(square,circle).
diff_shape(circle,triangle).
diff_shape(triangle,circle).
diff_shape(square,triangle).
diff_shape(triangle,square).
