Write a function equivs of the type ('a -> 'a -> bool) -> 'a list -> 'a list list, which par- (6) titions a list into equivalence classes according to the equivalence function.

a study funded by private corporations refuting global warming

only #2 represents an object at rest on a table.

in #1, there is no normal force due to the table; the object is accelerating downward.

in #3, the vertical forces are not balanced; the object is accelerating downward.

in #4, neither the vertical nor the horizontal forces are balanced. the object is accelerating upwards and to the right.