  Magnus' Freiheitssatz states that if a group is defined by a presentation
with $m$ generators and a single relator containing the last generating letter,
then the first $m-1$ letters freely generate a free subgroup. We study an
analogue of this theorem in the Gromov density model of random groups, showing
a phase transition phenomenon at density $d_r = \min\{\frac{1}{2},
1-\log_{2m-1}(2r-1)\}$ with $1\leq r\leq m-1$: we prove that for a random group
with $m$ generators at density $d$, if $d < d_r$ then the first $r$ letters
freely generate a free subgroup; whereas if $d > d_r$ then the first $r$
letters generate the whole group.
