We show that any free *-autonomous category is equivalent (in a strict sense) to a free *-autonomous category in which the double-involution $(-)^{**}$ is the identity functor and the canonical isomorphism $A\simeq A^{**}$ is an identity arrow for all $A$.
2000 MSC: 03F52,18D10,18D15
Theory and Applications of Categories,
Vol. 17, 2006,
No. 2, pp 17-29.
http://www.tac.mta.ca/tac/volumes/17/2/17-02.dvi
http://www.tac.mta.ca/tac/volumes/17/2/17-02.ps
http://www.tac.mta.ca/tac/volumes/17/2/17-02.pdf
ftp://ftp.tac.mta.ca/pub/tac/html/volumes/17/2/17-02.dvi
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