Superposition Operators in the Algebra of Functions of Two Variables with Finite Total Variation

 We show that the Hardy space of functions of two variables with finite total variation is a Banach algebra under the pointwise operations and a suitably chosen norm. Then we characterize Nemytskii superposition operators, which map the Hardy space into itself and satisfy the global Lipschitz condition. Received 7 June 2001; in revised form 8 January 2002