I develop a module for the solution of a set of equations,
where no complex combinations of equations must be considered,
but only an admissible order of single equation solutions.
This wouldn't be much of a problem,
but we like to let the Lazy Evaluator of Haskell do the work.
The idea evolves along several modules, which are in chronological order:

ListMaybe
Peano
SingleStep




ToDo:

- Equations must be checked lazily.
  In order to work-around precision problems with floating point numbers
  an equation should be considered as fulfilled,
  if one of the equivalent formulations hold.

- If a variable is undefined by the equations system, it is undefined. :-)
  To be more precise: We run into an infinite loop.
  Is there a way to detect undefined values
  and give a proper error report?