If an abelian topological group
(G,t) satisfies Pontryagin duality, then the t-compact subsets and the weak compact
subsets coincide. Hence if t1,t2 are group topologies on an abelian.group G such that
(G,ti)i = 1,2 satisfy Pontryagin duality and have the same set of continuous
characters, then t1= t2.