{ my %used;       # module => 1 if require ok, 0 otherwise
  my %disallowed; # for testing, refuses to _use modules in this hash

  sub _disallow_use
    { my( @modules)= @_;
      $disallowed{$_}= 1 foreach (@modules);
    }

  sub _allow_use
    { my( @modules)= @_;
      $disallowed{$_}= 0 foreach (@modules);
    }

  sub _use
    { my( $module, $version)= @_;
      $version ||= 0;
      if( $disallowed{$module})   { return 0; }
      if( $used{$module})         { return 1; }
      if( eval "require $module") { import $module; $used{$module}= 1; 
                                    no strict 'refs';
                                    if( ${"${module}::VERSION"} >= $version ) { return 1; }
                                    else                                      { return 0;  }
                                  }
      else                        {                 $used{$module}= 0; return 0; }
    }
}