 Other structural modifications vary the name as usual in systematic nomenclature, so a [4.6.4.6]fenestradiene has two cyclobutane rings and two cyclohexane rings in an alternating pattern and two alkene units in the ring structure.In addition to the ring sizes, fenestranes can have various combinations of cis and trans geometry at each ring fusion.These details are denoted by ""c"" and ""t"" prefixes to the structure name, listed in the same order as the ring-sizes.