class Time

def to_s_lex(precision = :day)

return:: a lexicographically sortable string representing the date
options are :year, :month, :day, :hour, :minute and :second
precision:: the precision required in the string version of the time. The

precision. The format used is %Y%m%d %H:%M:%S.
Convert the Time to a lexicographically sortable string with the required 
def to_s_lex(precision = :day)
  self.strftime(LEX_FORMAT[precision])
end