This can be established by purely mechanical means, such as by throwing identical billiard balls with equal force in various directions (so that the net impulse to the thrower is zero), and assuming that inertia is isotropic.
(This; can be established; by purely mechanical means, such as) (the net impulse to the thrower; is; zero)
This the net impulse to the thrower
can be established is
by purely mechanical means, such as
zero