A fixed point technique for approximate a functional inequality in normed modules over C*-algebras

In this paper, we apply fixed point technique to investigate the following additive functional inequality: ||f(x)+f(y)+f(z)+f(w)||?||f(x+y)+f(z+w)|| in normed modules over a C*-algebra, which is also applied to understand homomorphisms in C*-algebras. Our results improve and generalize some results given by some authors. Especially, we get a better error estimation of An?s main result.

Approximate generalized additive mappings in proper multi-CQ*-algebras

In this paper, we approximate the following additive functional inequality ?( ?d+1,i=1 f(x1i),..., ?d+1,i=1, f(xki))? ? ?mf (?d+1,i=1 x1i/m),..., mf (?d+1,i=1 xki/m)) ?k for all x11,..., xkd+1?X. We investigate homomorphisms in proper multi-CQ*-algebras and derivations on proper multi-CQ*-algebras associated with the above additive functional inequality.