When streets are dedicated to the city, the city retains a fee simple determinable. At such time as the city vacates a street, avenue, alley, or lane, the land within such street or alley reverts to the owners of the adjacent real estate, one-half on each side thereof. Belgum v. City of Kimball, 163 Neb. 774, 81 N.W.2d 205 (1957).