Complex sentence: In 1955, she completed a master thesis on "Multiplicative Lattices with Additive Basis" under the supervision of Petr Grigor'evich Kontorovich, before returning to Bucharest to join the faculty of Mathematics at the Polytechnic Institute of Bucharest.
Split into simpler sentences: In 1955, she completed a master thesis on "Multiplicative Lattices with Additive Basis" under the supervision of Petr Grigor'evich Kontorovich. Kreindler returned to Bucharest where she joined the the faculty of Mathematics at the Polytechnic Institute of Bucharest.