  A contraction-free and cut-free sequent calculus $\msf{G3SDM}$ for semi-De
Morgan algebras, and a structural-rule-free and single-succedent sequent
calculus $\msf{G3DM}$ for De Morgan algebras are developed. The cut rule is
admissible in both sequent calculi. Both calculi enjoy the decidability and
Craig interpolation. The sequent calculi are applied to prove some embedding
theorems: $\msf{G3DM}$ is embedded into $\msf{G3SDM}$ via G\"odel-Gentzen
translation. $\msf{G3DM}$ is embedded into a sequent calculus for classical
propositional logic. $\msf{G3SDM}$ is embedded into the sequent calculus
$\msf{G3ip}$ for intuitionistic propositional logic.
