risers (x:y:etc) 
  = if x <= y then (x:s):ss else [x]:(s:ss)
    where (s:ss) = risers [] -- insert partiality (y:etc)
risers (x:y:etc) 
  = if x <= y then (x:s):ss else [x]:(s:ss)
    where (s:ss) = risers [] -- insert partiality (y:etc)
risers (x:y:etc) 
  = if x <= y then (x:s):ss else [x]:(s:ss)
    where (s:ss) = risers [] -- insert partiality (y:etc)