The representation of key expressions is very simple and makes it easy to construct new keys on the fly.
Objects are represented by their object numbers and all other kinds of key expressions are represented by lists. These lists have as their first element a string drawn from the following set:
"&&" "||" "!" "?"
For the first two of these, the list should be three elements long; the second and third elements are the representations of the key expressions on the left- and right-hand sides of the appropriate operator. In the third case, "!", the list should be two elements long; the second element is again a representation of the operand. Finally, in the "?" case, the list is also two elements long but the second element must be an object number.
As an example, the key expression
#45 && ?#46 && (#47 || !#48)
would be represented as follows:
{"&&", {"&&", #45, {"?", #46}}, {"||", #47, {"!", #48}}}