Which statements are equivalent to the following For all nodes x and y, if x is before y and x = y, then y is not before x. Select one or more: O a. For all nodes x and y, where x + y, if x is before y, then y is not before x. O b. For all nodes x and y, x is before y and x + y and y is not before x. o O o c. For all nodes x and y, if y is not before x, then x is before y and x + y. d. For all nodes x and y, if x is before y and y is before x, then x = y. e. For all nodes x and y, if x is before y, then y is not before x