This alternative version of disambiguate.crit2 implements the following

This alternative version of disambiguate.crit2 implements the following
criterion for spurious error detection:

an error is spurious iff:
  a) it is obtained interpreting the symbol s with the interpretation \phi
  b) there exists another interpretation \phi' such that
     1) dom(\phi) = dom(\phi')
     2) \phi' is valid
     3) \phi(x)=\phi'(x) for each x != s

More (but not too many) errors are spurious according to this criterion.