ABSTRACT
Which groups with four elements do we know? Well, for example the additive group ℤ4, the multiplicative group {±1,±i}, and the symmetry groups of the figures F 1 and F 2 below. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315136547/a57ae1f0-6f59-46bd-bbdd-35a521b486a1/content/page511_1.tif"/>
