def _periodicity(args, symbol):
 periods = []
 for f in args:
  period = periodicity(f, symbol)
  if (period is None):
   return None
  if (period is not S.Zero):
   periods.append(period)
 if (len(periods) > 1):
  return lcim(periods)
 return periods[0]

def _periodicity ( args , symbol ) : periods = [ ] for f in args : period = periodicity ( f , symbol ) if ( period is None ) : return None if ( period is not S . Zero ) : periods . append ( period ) if ( len ( periods ) > 1 ) : return lcim ( periods ) return periods [ 0 ]
helper for periodicity to find the period of a list of simpler functions .