# What does the term “inversion symmetric” mean?

I've read the responses to the question `"Lack of inversion symmetry" in crystal?' but I'm still unsure about the meaning of inversion symmetry. Which of the following two dimensional shapes are inversion symmetric?

(a) $\longleftrightarrow$

(b) $\leftharpoonup\rightharpoondown$

(c) $\leftharpoonup\rightharpoonup$

(d) $\nleftarrow\nrightarrow$

• Space inversion is also known as the parity transformation, and inversion-symmetric systems are sometimes called parity-symmetric or parity-conserving systems. – rob Apr 9 '18 at 18:23
• More precisely, space inversion and parity differ by a rotation in the plane relative which the parity transformation is performed. – mavzolej Apr 17 at 4:41

I believe it means that the transformation $$\textbf{r}\rightarrow -\textbf{r}$$ produces the same figure. That is, if you see a point at $$(x,y,z)$$ you should also see one at $$(-x,-y,-z)$$.