The variables mentioned above do not currently exist but the underlying requirement for something like this is on our list for the next major release. Most likely we are going to be implementing more of a formula language for our variables so that you can make it do whatever you want but we're still working out the details. In the meantime, what I typically recommend for people is to just create a copy of the Crystal Report they are trying to use these variables with and simply make use of the Select Expert to develop very powerful formulas. For example, if you have a report that prompts for a Start Date and End Date and you want to schedule it to run for the previous months data automatically you couldn't do this as-is with Logicity. However, if you copied this report and switched the Select Expert from using parameter input to just the Date = LastFullMonth then it could at least allow you to do what you need for the time being.
Hope this helps!