== Expressing integers using four nines
What non-negative integers can you write as expressions containing exactly four occurrences the number 9, and any of the binary operators *, /, %, +, -, prefix negations, and any number of matching pairs of parentheses you care to use?
The program should accept an upper limit N as a command-line argument. It should then print all integers 0..N in increasing order, along with an expression with four nines, if any such was found.