Another nice concept: normal numbers. These are numbers which have a very basic property of randomness: getting the block frequencies right. [1] The strong law

Another nice concept: normal numbers. These are numbers which have a very basic property of randomness: getting the block frequencies right. [1] The strong law of large numbers implies that almost every number in the unit interval is normal. Giving a simple construction of a normal, and proving that it is indeed normal, is quite difficult. [1] https://en.wikipedia.org/wiki/Normal_number https://en.wikipedia.org/wiki/Normal_number