The reason for rules - the mediator remembered from his lectures as a trainee - is not to stop you from doing whatever it is but to think about the possible consequences before you do.

Remediation Protocols 101 had the most emphasis on the danger of Time Line Interference. That this was completely forbidden under any circumstances was constantly reiterated, which greatly clarified possible exceptions to the rule.

What wasn't said, even though most trainee mediators found out soon enough, was that exceptions to the rule often occurred of their own volition. If it happened on your watch you would be for the high jump unless you had cast iron proof it wasn't because of anything you'd done.

A course of study at the Pratchett Institute for advanced time management taught how important it was to become familiar with Time Slicing and the use of field procrastinators. The latter were the province of Lu Tse's History Monks who could be tiresome to invoke but were the best last resort if in need.

Time Lines often appeared to possess a mind of their own and could choose to bifurcate like a passing siding on a single track railway - a feature humorously known as the Trousers of Time- but that didn't promise the time line in question would revert to single track again. Indeed the testimony of one man whose personal organizer got stuck in the alternative was a testimony of disasters culminating in its (alternate) owners death.

Had he found himself down the wrong temporal trouser leg and that fate would have been his. Time doesn't care who pays the bill as long as it does get paid.

Learn to trust your instincts, the mediator firmly believed, his were making him uneasy about the painless perfect switch that Charles into Zefram seemed to be working out as. If it looks too good to be true then it is. murmured another aphorism accompanied by 'whatever can go wrong, will!'.