<range>  (<seq.>)  C 
rangeby  (from<num> test<fun> lim<num> by<fun>=> <range>)  G 
 returns a range starting from, updated with by,
and continuing until (test x lim) is false.  
range  (from<num> test<fun> lim<fun> => <range>)  G 
 == (rangeby from test lim (op + _ 1))  
from  (from<num> => <range>)  G 
 == (range from (always #t) 0)  
below  (lim<num> => <range>)  G 
 == (range 0 < lim)  
<step>  (<seq.>)  C 
 Steps represent step functions.  
firstthen  (first<fun> then<fun> => <step>)  G 
 returns a new step object, calling thunks first to retrieve
initial value and then to retrieve subsequent values.  
each  (f<fun> => <each>)  G 
 returns a new each object, calling f thunk to retrieve
each value.  
<cycle>  (<seq.>)  C 
 Cycles provide a mechanism to create infinite sequences repeating
a certain sequence over and over again.  
cycle  (x... => <cycle>)  G 
 returns a cycles that repeats elements of x.  
