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Suppose I have a list A={x1,x2,x3}, a list B={3,4,5}, and a function f[x]=x1+x2+x3. Is there a simple way to create a replacement rule R such that I can do a f[x]/.R to get 3+4+5?

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up vote 11 down vote accepted

Yes, there is a simple way: Thread.

x1 + x2 + x3 /. Thread[A -> B]

Other ways to create the list of replacement rules include

Rule @@@ Transpose[{A, B}]
MapThread[Rule, {A, B}]
Inner[Rule, A, B, List]

Or less obvious

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