  We give a transformation between the off-shell field variables of Witten's
open bosonic string field theory and the traditional lightcone string field
theory of Kaku and Kikkawa, based on Mandelstam's interacting string picture.
This is accomplished by deforming the Witten vertex into lightcone cubic and
quartic vertices, followed by integrating out the ghost and lightcone
oscillator excitations from the string field. The surprise is that the last
step does not alter the lightcone interactions or generate effective vertices,
and leads precisely to Kaku and Kikkawa's lightcone string field theory.
