Comment on “A theorem for a shear stress-free plane boundary in Stokes flow”

The results proved in a recent paper by Akhtar and Sen Mech. Res. Commun. 38 (2011) 529–531] are not new and are already known in the literature. In fact, the main expressions – presented in the form of a theorem – in the cited article follow as a special case of the more general results for a two-fluid Stokes flow with a planar interface proved earlier by Palaniappan Acta Mechanica 139 (2000) 1–13]. We briefly demonstrate the reduction of particular cases of the solution given by Palaniappan which also reveals the duplication of another special solution elsewhere.