(geometry) a theorem stating that if a set of points P_i lying on a line is isometrically mapped to points P_i' on a different line, then the midpoints of the segments P_iP_i' also lie on a line.

Not affirmative.

Something that can be claimed.

(organic chemistry) The divalent radical CH₃-CH₂-CH< analogous to ethylidene; propylidene / (organic chemistry) The pesticide butan-2-yl 2-(2-hydroxyethyl)piperidine-1-carboxylate