12. Determine the volume of the triangular pyramid $S A B C$, if in it $S A=S B=S C=1 ; \angle A S B=60^{\circ}, \angle A S C=90^{\circ}$ and $\angle B S C=120^{\circ}$.
12. The volume of the triangular pyramid $S A B C$ is $v=\frac{\sqrt{6}}{6}$ (cubic units).