Canonical Zchar_opprPred := OpprPred Zchar_zmod.
Canonical Zchar_addrPred := AddrPred Zchar_zmod.
Canonical Zchar_zmodPred := ZmodPred Zchar_zmod.

Lemma zchar_subseq S1 S2 A :
subseq S1 S2 -> {subset 'Z[S1, A] <= 'Z[S2, A]}.