{\bf Abstract}

Isometries on formal power series over the finite field \ff_2
or on 2--adic integers can be
computed by invertible transducers on inputs from \{0,1\}^\infty.
We consider the structural complexity of an isometry f,
measured as {\it tree complexity} T(f,h), h the tree height
[H.~Niederreiter, M.~Vielhaber, {\it J.~Cpx.}, ... more >>>