Quantization replaces each real number with an approximation from a finite set of discrete values. Digital circuits are electric circuits based on a number of discrete voltage levels. The definition generalizes to a mixture of arbitrary numbers of discrete and continuous random variables. This substantially unifies the treatment of discrete and continuous probability distributions. Weight functions can be employed in both discrete and continuous settings. Hybrid systems are those that mix discrete and continuous behavior. We use cumulative distribution functions (cdf) in order to encompass both discrete and continuous distributions. The probability amplitude supports calculation of probability of location or momentum of discrete particles. Examples of problems involving discrete variables include integer programming. Combinatorics concerns the study of discrete (and usually finite) objects. Hybrid systems allow for time domains that have both continuous and discrete parts. Furthermore, it covers distributions that are neither discrete nor continuous nor mixtures of the two. Note that similar rules apply to either discrete or continuous cases. There exist groups for which computing discrete logarithms is apparently difficult. See Cumulants of some discrete probability distributions.