For a topological group, the quotient map modulo a subgroup is open and the quotient map modulo a compact subgroup is perfect. In this paper we prove and develop the corresponding compact-ideal theory for topological -algebras. We show that if is an ideal of a topological -algebra , then the natural quotient homomorphism , where is endowed with the quotient topology, is a continuous open quotient map and is again a topological -algebra. If, in addition, is compact, then is perfect. As applications, we study three-space phenomena in topological -algebras. Under compact-kernel hypotheses we prove three-space theorems for compactness, local compactness, -compactness, Lindelöfness and paracompactness under the separation hypotheses stated below. We also prove a first-countability three-space theorem for locally convex topological -algebras.

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