Function to enumerate an minimal count of occurrences
atLeast(x, query, aperture = duringInterval(eventStarts(-Inf, Inf)))
the integer counting the number of occurrences
a query object that provides context to the clinical event of interest
an eventAperture object that shows the temporal span where the event is to be observed relative to the index event
A criteria that can be used in a cohort definition specifying satisfaction of at least x instances of a query