clarified Event_Timer.shutdown: manager thread remains until final shutdown in Session.finish; discontinued spontaneous thread expiration from TTY age to avoid sporadic Simple_Thread.fork, which is potentially fragile in situations of resource shortage;

ignore print process even after fork, to avoid loosing active worker threads;

rel_pmf OO: conversion to nat is not necessary

merged

simplify construction for distribution of rel_pmf over op OO

prefer option for default code printing width

modernized and more uniform style

tuned order

tuned

avoid technical term "mixin" in user documentation text