Correlation inequalities are presented for ferromagnetic Potts models with external
field, using the random-cluster representation of Fortuin and Kasteleyn,
together with the FKG inequality. These results extend and simplify earlier
inequalities of Ganikhodjaev and Razak, and also of Schonmann, and
include GKS-type inequalities when the spin space is taken as the set of
-th
roots of unity.