Complex sentence: He studied art at the then Chelsea Polytechnic from 1936--9 and once again from 1946--7 under Ceri Richards, Robert Medley, Harold Williamson and Raymond Coxon.
Split into simpler sentences: He studied art at the then Chelsea Polytechnic from 1936--9. His tutors were Ceri Richards, Robert Medley, Harold Williamson and Raymond Coxon.