Simplified method	void process_expression(const ExtendedExpression * elt_left,const ExtendedExpression * elt_right)
Simplified constructor ConcatExpr(const ExtendedExpression * expr_left, const ExtendedExpression * expr_right)
Removed the bug abb ->ab and abba -> aba bug
Added automatic check of canonical rewrite rules uu# -> u# u#u#->u# u#u->u#
Added distinct printing of canonical and non-canonical rewrite rules