No, there was never a difference in the football size or regulations between the AFC and NFC. This would be too hard to regulate since the AFC and NFC teams play each other so often.
Allosteric regulation and Reversaeble regulation :)
exist is = to be excist = nothing
A hamtet does not exist.
A problem is what exists when there is a difference between the current situation and the desired one.
Regulation act
The main difference is that a triangle rectangle cannot exist.
Any chemical difference exist.
- protons are positive and neutrons are neutral- a small difference of mass exist
Any difference exist. A simple solution may be a diluted solution.
polarized
One is an Australian Marsupial (kangaroo); the other does not exist.
HCO3- is a anion (bicarbonate); HCO3+ don't exist.