With regard to double patenting, we recently explained that 35 U.S.C. § 121 (1988) will not apply to remove the parent as a reference where the principle of consonance is violated: Consonance requires that the line of demarcation between the "independent and distinct inventions" that prompted the restriction requirement be maintained. Though the claims may be amended, they must not be so amended as to bring them back over the line imposed in the restriction requirement. Where that line is crossed the prohibition of the third sentence of Section 121 does not apply.
Symbol Technologies, Inc. v. Opticon, Inc., 935 F. 2d 1569, 1579 (Fed. Cir. 1991)