Galois module structure of Type I (ii) for units in biquadratic number fields (reviewed)

The notation follows Mazur and Ullom, Galois module structure of units in real biquadratic number fields, Acta Arithmetica 111.2 (2004) [10.4064/aa111-2-1, MR:2039416]. There are four basic types, I-IV, which describe the structure of the units $U$ modulo roots of unity. The subtype describes the actual structure of the units. Type I (ii) means that there are fundamental units $e_1,e_2,e_3$ of the three quadratic subfields such that $\sqrt{e_1},e_2,e_3$ generate the rank 3 group $U/\{\pm 1\}$.