Examples of this lack of meaning include statements about the existence or nonexistence of God. Alex says the impending threat of nonexistence invalidates morality. Conflicting claims regarding both the kingdom's extent and arguable nonexistence were pursued in diplomatic exchanges. The nonexistence of an asymptotically optimal algorithm is called speedup. He gives the example that nothing can go from nonexistence to existence. Einstein was noncommittal to aether's nonexistence, simply said it superfluous. Motahhari defined freedom as nonexistence of obstacles. Melissus claimed that reality was "full" (nonexistence being impossible), and that therefore nothing could move. Acland has spoken and written about the nonexistence of Subliminal Perception. However, the nonexistence of a compass-and-straightedge solution was finally proven by Pierre Wantzel in 1837. This is evident due to the virtual nonexistence of HIV transmission through oral-to-oral contact.