D=10 supersymmetric Yang-Mills theory at alpha'^4

The $\alpha'^2$ deformation of D=10 SYM is the natural generalisation of the $F^4$ term in the abelian Born-Infeld theory. It is shown that this deformation can be extended to $\alpha'^4$ in a way which is consistent with supersymmetry. The latter requires the presence of higher-derivative and commutator terms as well as the symmetrised trace of the Born-Infeld $\alpha'^4$ term.
Comment: 27 pages. Minor changes to text; references added.