Lambda the Ultimate

I've got two tuples

  Ta = (a0, a1, ..., aM)
  Tb = (a0, a1, ..., aN)

With the subtyping relationship

  Ta <: Tb

I am interested in referring to the type difference, and I was thinking of notating it as:

  Ta \ Tb = (aM, aM+1, ..., aN)

Is there a standardized notation or language for referring to such a concept?

Chris Oliver has been blogging about F3, a soon-to-be-open-sourced functional programming framework for Java. It's statically typed, comes with an Eclipse plugin, and does some pretty cool dataflow/dependency management. It reminds me of SuperGlue, from McDirmid and Hsieh.