Hard Edge Abstraction was a movement of international contemporary art that developed during the 1960s. It typically involved large geometric forms in flat colours.
Putting it on Pelican covers was part of a tendency at the publisher from the late 1960s towards abstract cover designs. It branded the book as contemporary and stylish and must have adapted well to face-forward bookshop display.
//…. These two covers from 1976 and 1978 are by Eugenio Carmi, a renowned Italian artist whose style in the 1970s had swung around to this form of cool geometric abstraction. The images below are paintings from that period.