Problem understanding half wave symmetry I am trying to understand half wave symmetry.

I understand the first (a) graphical image is half wave symmetry but (b) seems like even symmetry and (c) seems to be odd symmetry. I am unable to find the difference. Please guide.
Edit: I read my question and it seems to be confusing. I know the b is even symmetry and c is odd but how are they half wave symmetry?

one more point to add to the above answer:
what is the difference between even half wave symmetry and an even signal and similarly for odd?
for a signal to be half wave symmetric the area under the curve for one period should be 0. it is not necessary for an even or odd signal
