[Tutor] regular expression question

[Mike Hall]

I'd like to get a match for a position in a string preceded by a 
specified word (let's call it "Dog"), unless that spot in the string 
(after "Dog") is directly followed by a specific word(let's say "Cat"), 
in which case I want my match to occur directly after "Cat", and not 
"Dog."

I can easily get the spot after "Dog," and I can also get it to ignore 
this spot if "Dog" is followed by "Cat." But what I'm having trouble 
with is how to match the spot after "Cat" if this word does indeed 
exist in the string.
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