  We show that IIA supergravity can be extended with two independent 10-form
potentials. These give rise to a single BPS IIA 9-brane. We investigate the
bosonic gauge algebra of both IIA and IIB supergravity in the presence of
10-form potentials and point out an intriguing relation with the symmetry
algebra $E_{11}$, which has been conjectured to be the underlying symmetry of
string theory/M-theory.
