Uncertainties in (English) Notation

[Guy Steele <cbmvax!uunet!Think.COM!gls>]

   From: cbmvax!snark.thyrsus.com!cowan@uunet.UU.NET (John Cowan)
   Date: Tue, 16 Apr 91 11:29:43 EDT

   I wrote, in the EBNF grammar explanations:

   > The elidable terminators make the language unambiguous, but may often be
   > omitted without loss of ambiguity, especially when there is more than one
   > in a row.

   Doug Landauer <landauer@eng.sun.com> rewrote this as:

   > 	The elidable terminators, when present, make the language
   > 	unambiguous.  However, they may often be omitted without
   > 	making an utterance ambiguous, especially when there are
   > 	more than one in a row.

   That's more like it.  "Loss of ambiguity" should have been just "ambiguity".
   In addition, the confusion over whether "elidable" was descriptive (as I
   intended) or defining (as Guy Steele assumed) made matters worse.

Better, but I still find it problematical.

The ET's, when present *in the language*, make the *language* ambiguous.
The ET's, when present *in an utterance*, make the *utterance* unambiguous
  (because their inclusion in an utterance avoids the problem in the language).

--Guy