Given a finite sequence of digits, we consider the question whether this
sequence can be turned into a valid equality, by inserting operations
+ , - , * and /, brackets and one equality sign between each of the digits.
Is it so that from a certain length onwards, all sequences can be turned
into such an equation?
In order to answer this question, we consider another predicate: can a
sequence of digits be turned into an an expression denoting 0?

For these two questions we develop a little mathematics, and using these
results we developed a computer program that gives some concrete results.
All sequences longer than 7 digits can indeed yield zero: the greatest sequence
that cannot yield zero is 8985898. All sequences longer than 8 digits can
yield a valid equality: the greatest sequence which cannot is 98589808.