JEAN BIRKENSTEIN WASHINGTON's life as dominated by a dedication to civil rights and racial equality, an uncompromising respect for nature and a near-obsessive fascination for mathematics and physics. The constant through which she most fully expressed these divergent elements was her art -- more than half a century of paintings, drawings and sculpture that capture the sorrow of slavery and imprisonment, the view of urban America from a feline perspective and, in abstracts and still lifes, a distillation of physical space into its geometric building blocks and mathematical essence.