+- Warn when left-recursive symbols appear elsewhere, other than at the end
+ of a production. Might have to special-case Newlines.
+- parser not to get into ERROR infinite loop
+- sort 'virtual' symbols to end
+- allow $xy instead of $3. Chooses shortest bodysym with xy in that order
+ $xy_2 gives the second one
+- allow $TERM terminals to be listed. If so, extras are errors