  An ab-initio calculation of the 4He(e,e') inelastic longitudinal response
function R_L is presented. Realistic two- and three-body forces are used. The
four-body continuum dynamics is treated rigorously with the help of the Lorentz
integral transform. The three-nucleon force reduces the quasi-elastic peak
height by about 10% for momentum transfers q between 300 and 500 MeV/c.
Experimental data are well described, but not sufficiently precise to resolve
this effect. The reduction due to the three-nucleon force increases
significantly at lower q reaching up to about 40% at q=100 MeV/c. However, at
such q values data are missing.
