def isSkip(n1, n2): return And( Interval.absBetween(n1, n2) >= Interval(3), Interval.absBetween(n1, n2) <= Interval(6))
def isLeap(n1, n2): return Interval.absBetween(n1, n2) >= Interval(7)
def isStep(n1, n2): return Or( Interval.absBetween(n1, n2) == Interval(1), Interval.absBetween(n1, n2) == Interval(2))