sentences:  Over time, her primary research efforts went increasingly into control theory, and in 1968, the year of her retirement, she published her second book, "Discontinuous and Optimal Control".By the mid-1950s, it became evident that Flügge-Lotz was performing all the duties of a full Professor but without official recognition.In fact, it was hard for students to understand why she was a Lecturer rather than a Professor, or even what the difference meant.