On the first use, define the first {motion} to exchange. On the second use, define the second {motion} and perform the exchange.
`cxc`
Clear any {motion} pending for exchange.
Example
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To exchanges two words, place your cursor on the first word and type `cxiw`. Then move to the second word and type `cxiw` again. Note: the {motion} used in the first and second use of `cx` don't have to be the same.