:- expects_dialect(lps). maxTime(10). withinPeriod(First-Last) at T if T >= First, Last >= T. actions a(_). if withinPeriod(3 - 7) at T then a(hello/T) from T. if true then withinPeriod(3 - 7) at T1, a(hi/T1) from T1 to T2, a(hi2/T2) from T2, fail.