  We propose 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. Surprisingly, the last step does
not alter the cubic and quartic interactions and does not generate effective
vertices, and leads precisely to Kaku and Kikkawa's lightcone string field
theory.
