On the Automorphisms of Some One-Relator Groups
  The description of the automorphism group of group $<a, b; [a^m,b^n]=1>$ ($m,n>1$) in terms of generators and defining relations is given. This result is applied to prove that any normal automorphism of every such group is inner. 
D. Tieudjo and D.I. Moldavanskii