old_contents: """
  This is the pyro multigrid solver.  It uses a second-order discretization
  of a constant-coefficient Helmholtz equation:
  
   (alpha - beta L) phi = f
  
  and pure V-cycles to solve elliptic problems
  """
  
  __all__ = ['MG', 'variable_coeff_MG']
  
  
new_contents: """This is the pyro multigrid solver.  THere are several versions.
  
  MG implements a second-order discretization of a constant-coefficient
  Helmholtz equation:
  
   (alpha - beta L) phi = f
  
  
  variable_coeff_MG implements a variable-coefficient Poisson equation:
  
    div { eta grad phi } = f
  
  general_MG implements a more general elliptic equation:
  
    alpha phi + div { beta grad phi } + gamma . grad phi = f
  
  
  All use pure V-cycles to solve elliptic problems
  
  """
  
  __all__ = ['MG', 'variable_coeff_MG']
  
subject: update docstring