- notation (possibly affecting all .ma files):

  we shifted the precedence levels from 50 to 60 up by 5
  and moved level 65 to 66. By so doing, we cleared level 50 for
  use in the specification of the formal system lambda_delta,
  where we use it for weakly binding constructors
- lambda_delta:
  notation fixup (a couple of bugs were corrected)