A line-mending reaction is a mechanism that can fully mend a sealed gap in an infinite diagonal line of cells, such as the one produced by a line-cutting reaction. Such a reaction is demonstrated below, in two stages. The second stage can be subdivided if necessary, at the cost of two additional gliders. See BNE14T30 for one way of creating the gliders travelling parallel to the lines.
x = 135, y = 135, rule = B3/S23
2o$o$bo$2bo$3bo$4bo$5bo$6bo$7bo$8bo$9bo$10bo$2bo8bo$3b2o7bo$2b2o9bo$
14bo$15bo$16bo$17bo$18bo$19bo$20bo$21bo$22bo$23bo$24bo$18bo6bo$19bo6bo
$17b3o7bo$bo26bo$2bo26bo$3o27bo$31bo$32bo$33bo$34bo$35bo$36bo$37bo$38b
o$39bo$40bo$41bo$42bo$43bo$44bo$45bo$46bo$47bo$48bo$49bo$50bo$51bo$52b
o$53bo$54bo$55bo$56bo$57bo$58bo$59bo$60bo$61bo$60b2o10$71b2o$71bobo$
74bo$75bo$76bo$77bo$78bo$79bo$80bo$81bo$46b2o34bo$45bobo35bo$47bo22b2o
12bo$69b2o14bo$71bo14bo$87bo$78b2o8bo$77b2o10bo$79bo10bo$91bo$92bo$93b
o$94bo$95bo$96bo$97bo$98bo$99bo$100bo$13b2o86bo$14b2o86bo$13bo89bo$
104bo$21b2o82bo$20bobo83bo$22bo84bo$108bo$109bo$110bo$26b3o82bo$12b2o
14bo83bo$13b2o12bo85bo$12bo93b2o6bo$106bobo6bo$106bo9bo$117bo$6b2o23bo
86bo$7b2o11bo10b2o86bo$6bo13b2o8bobo87bo$19bobo99bo$122bo$123bo$124bo$
14bo110bo$14b2o110bo$13bobo111bo$128bo$121bo7bo$120b2o8bo$103b2o15bobo
8bo$103bobo26bobo$103bo29b2o!
#C [[ THUMBSIZE 2 THEME 6 GRID GRIDMAJOR 0 SUPPRESS THUMBLAUNCH ]]
#C [[ AUTOSTART X -7 Y 7 Z 3 PAUSE 2 GPS 25 HEIGHT 480 LOOP 300 THUMBLAUNCH THUMBSIZE 2 T 240 X -1 Y 10 Z 8 T 299 X -7 Y 7 Z 3 PAUSE 2 ]]