Complex sentence: In 1969-70 he was a Visiting Professor at Purdue University in the USA by the invitation of Victor J. Papanek and was a close collaborator of Papanek for several years.
Split into simpler sentences: In 1969-70 he was a Visiting Professor at Purdue University in the USA by the invitation of Victor J. Papanek. He was a close collaborator of Papanek for several years.