grid.sass

=x-omega($n, $context: false)
  +float($omega-float)
  width: columns($n, $context)
  @if $context
    margin-right: 0
  @else
    margin-right: side-gutter()
  @if $hacks
    +ie-omega($omega-float, true)

=x-alpha($n, $context: false)
  +columns($n, $context)
  @if not $context
    margin-left: side-gutter()

input.sass

#old-omega
  +columns(3,6)
  +omega(6)

#new-omega
  +x-omega(3,6)

#old-alpha
  +columns(3,6)
  +alpha(6)

#new-alpha
  +x-alpha(3,6)

output.css

#old-omega {
  display: inline;
  float: left;
  width: 48.276%;
  margin-right: 3.448%;
  display: inline;
  float: right;
  margin-right: 0;
  /* ugly hacks for IE6-7 */
  #margin-left: -1em;
}

#new-omega {
  display: inline;
  float: right;
  width: 48.276%;
  margin-right: 0;
  #margin-left: -1em;
}

#old-alpha {
  display: inline;
  float: left;
  width: 22.951%;
  margin-right: 1.639%;
  margin-left: 1.639%;
}

#new-alpha {
  display: inline;
  float: left;
  width: 22.951%;
  margin-right: 1.639%;
  margin-left: 1.639%;
}