<正> Let K be a skew field and Z be its center.The multiplicative groups of non-zero ele-ments of K and Z are denoted by K~* and Z~* respectively.Denote by GL_2(K) the groupof all 2×2 matrices over K and by PGL_2(K) the factor group of GL_2(K) modulo its ce-nter consisting of all elements of the form γI,where γ∈Z~* and I is the 2×2 identitymatrix.If K is commutative or is of characteristic≠0 the automorphisms of PGL_2(K)are already determined.In the present paper,we'll determine the automorphisms of PGL_2(K)
<正> We use γ=(γ_(11),…γ_(t1),…γ_(15)…,γ_(ts))to denote a point in st-dimensionalEuclidean space R_(st).We use the notations γ_i=(γ_(li)…γ_(ti)(1≤i≤s)and γ_i=(γ_i1,…,γ_(is))(1≤j≤t).q=(q_1,…,q_t),k=(k_1,…,k_s)and m=(m_1,…,m_s)will be