15.  fragment address

|=  [nedl=* hay=*]
=/  count=@  1
|-  ^-  (unit @)
?:  =(nedl hay)
  [~ count]
?@  hay  ~
=/  head-search  $(hay -.hay, count (mul 2 count))
?~  head-search
  $(hay +.hay, count +((mul 2 count)))
head-search

16.  find and replace first fragment match

|=  [nedl=* hay=* new=*]
^-  *
?:  =(nedl hay)  new
?@  hay  hay
=/  new-head  $(hay -.hay)
?:  =(new-head -.hay)
  [-.hay $(hay +.hay)]
[new-head +.hay]

17.  find and replace all fragment matches

|=  [nedl=* hay=* new=*]
^-  *
?:  =(nedl hay)
  new
?@  hay  hay
:-  $(hay -.hay)
$(hay +.hay)