Volstrup

Poul Anderson, The Shield Of Time (New York, 1991).

In 1137, Everard visits Emil Volstrup in Palermo some time after King Roger of Sicily has escaped alive from the battlefield at Rignano and has continued to wage his war in Italy.

Previously (not previously in the current timeline but previously according to his own memory), Everard had conversed with Volstrup in 1137alpha after Roger had been killed at Rignano. The time traveling Everard has intervened at the battle and prevented that death. Thus, no one living in Palermo in 1137 should remember a death of Roger at Rignano - but Volstrup does. The explanation given is as follows:

"He alone in the city had experienced Everard's previous visit; in the course of that salvage operation he had twice been brought downtime for consultation." (p. 375)

"Everard's previous visit..." occurred not previously in the current timeline but in the previous timeline, in 1137alpha. If Volstrup traveled from a time after "'...the turning point...'" (p. 316), i.e., the death of Roger, to a time before it, then his memory of Roger's death would travel back with him. If he then traveled forward to a time after Everard's prevention of Roger's death, then he would still remember the death, even though he was now in a timeline where that death had not happened.

However, he would now coexist with a Volstrup who had not heard of Roger's death, had not previously been visited by Everard and had not "...been brought downtime for consultation." (see above) Poul Anderson in private correspondence accepted my argument that this procedure would have duplicated Volstrup. I think that, unless the Patrol worked very hard to prevent it, such duplications, intended or otherwise, would become a regular feature of their particular time travel scenario.

Anderson said that there might be a story idea here and also that there is more than one way that the Patrol might handle the situation but did not elaborate. Presumably it would be considered unethical to solve the problem by killing the spare Volstrup, whichever that is considered to be. One Volstrup could remain in place while the other worked for the Patrol elsewhen but how would the second Volstrup feel, for example, about leaving his wife?