Oscillation criteria for certain fourth order nonlinear functional differential equations

Some new criteria for the oscillation of the fourth order functional differential equation d d t ( 1 a 3 ( t ) ( d d t 1 a 2 ( t ) ( d d t 1 a 1 ( t ) ( d d t x ( t ) ) α 1 ) α 2 ) α 3 ) + δ q ( t ) f ( x [ g ( t ) ] ) = 0 , where δ = ± 1 are established.