This is a family of notations related to the big O notation. A good mnemonic summary of all notations would be:
Module bound above, possibly multiplied by a constant:
is defined as:
E.g.:
  • . For , is enough. Otherwise, any will do, the bottom line will always catch up to the top one eventually.
Stronger version of the big O notation, basically means that ratio goes to zero. In big O notation, the ratio does not need to go to zero.
So in informal terms, big O notation means , and little-o notation means .
E.g.:
  • K does not tend to zero