TeX source:

\rho_{AB} = \frac{1}{2}|0\rangle\langle0|_A\otimes|0\rangle\langle0|_B + \frac{1}{2}|1\rangle\langle1|_A\otimes|1\rangle\langle1|_B \quad\text{and}\quad \sigma_{AB} = |\text{EPR}\rangle\langle\text{EPR}|_{AB},