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    This is a new implemen
on of tidy, written in an attempt to remedy
    some of the deficiencies of 
old one.  Unfortunately, it has a few
    of its own.  The only complete
atisfactory approach seems to be to
    keep all expressions in bag 
 all the time.

    Tidy has now been split into two parts: tidy
t and tidy_expr.
	<stmt> ::= <stmt> # <stmt>	%   disjunction







































































































































































































































































































































































































































































































































 Bug fix: the user has always been able to add its
    own rewrite rules in the form simplify_axiom(Lhs, Rhs), e.g.
    simplify_axiom(X^log(X,Y), Y).  The result of this rewrite was
    assum



























































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































