  We present here a constructive method of Lagrangian approximate control-
lability for the Euler equation. We emphasize on different options that could
be used for numerical recipes: either, in the case of a bi-dimensionnal fluid,
the use of formal com- putations in the framework of explicit Runge
approximations of holomorphic functions by rational functions, or an approach
based on the study of the range of an operator by showing a density result. For
this last insight in view of numerical simulations in progress, we analyse
through a simplified problem the observed instabilities.
