Copyright © 2010 L. K. Kikina and I. P. Stavroulakis. This is an open access article distributed under the
Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Consider the second-order linear delay differential equation , , where , , is nondecreasing, for and , the (discrete analogue) second-order difference equation , where , , , , , and , and the second-order functional equation , , where the functions , , , for , , and denotes the 2th iterate of the function , that is, , , . The most interesting oscillation criteria for the second-order linear delay differential equation, the second-order difference equation and the second-order functional equation, especially in the case where and for the second-order linear delay differential equation, and and , for the second-order functional equation, are presented.