All-derivable points in the algebra of all upper triangular matrices

Let TMn be the algebra of all n×n upper triangular matrices. We say that an element G∈TMn is an all-derivable point of TMn if every derivable linear mapping φ at G (i.e. φ(ST)=φ(S)T+Sφ(T) for any S,T∈TMn with ST=G) is a derivation. In this paper we show that G∈TMn is an all derivable point of TMn if and only if G≠0.