Task 4

SCHEMA task4;
    ENTITY romb;
        color: OPTIONAL STRING;
        length: REAL;
        sharp_angle: REAL;
        WHERE
            side: length > 0.0;
            s_a: sharp_angle > 0.0 AND sharp_angle < 90
        DERIVE
            perimetr: REAL := 4*side;
    END_ENTITY;
END_SCHEMA.