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There was a novel I read back in the day about a boy who travels back and forth between a mirror-image of our universe.
I am afraid I cannot recall much about the plot, except that mirrored food is inedible and when mirrored ketchup packets were brought back from the other universe they taste like chocolate and mess you up.
Could someone help me identify this book?
After going through organic chemistry back in college, I think it should be required reading for any writer who has a story where the characters land on alien planets and find everything to be edible.