Number of elements in distribution for "discrete" type or number of
intervals of piecewise-linear density for "continuous" type.
If pdqr-function has "discrete" type and exactly two possible values 0 and
1, it is treated as "boolean" pdqr-function and probability of 1 is shown.
This is done to simplify interactive work with output of comparing functions
like >=, etc. (see description of methods for S3 group generic functions). To extract probabilities from "boolean"
pdqr-function, use summ_prob_true() and summ_prob_false().
Symbol "~" in print() output indicates that printed value or support is an
approximation to a true one (for readability purpose).