- In set terms Theta() is the intersection of O() and Omega() [more info at the highest ranked answer in [this complexity question](https://stackoverflow.com/questions/10376740/what-exactly-does-big-%D3%A8-notation-represent) on stackoverflow]. - Very few algorithms have Theta() (merge sort being one of the few examples), however all algorithms in the cheatsheet seem to have entries). - There also seems to be mixing between best, average, worst and the mathematical concepts of big Omega, Theta, O.