code: def _local_var_name(splittable_dimensions, assignment):
    
    assignment_string = []
    for splittable in sorted(splittable_dimensions):
      if splittable in assignment:
        assignment_string.append("{}:{}".format(splittable,
                                                assignment[splittable]))
      else:
        assignment_string.append("{}".format(splittable))
    return "y_(" + ",".join(assignment_string) + ")"
docs: Name for a local variable.
  
    Args:
      splittable_dimensions: frozenset of names of splittable dimensions.
      assignment: dict from names of splittable dimensions to names of mesh
        dimensions.
  
    Returns:
      A string, the variable name.