Homework Statement
Suppose that [\sigma_a]_{ij} and [\eta_a]_{xy} are Pauli matrices in two different two dimensional spaces. In the four dimensional tensor product space, define the basis:
|1\rangle=|i=1\rangle|x=1\rangle
|2\rangle=|i=1\rangle|x=2\rangle
|3\rangle=|i=2\rangle|x=1\rangle...