Note that #color(red)(16)# can and may be written as #color(red)(+12 + 4)#
So #color(green)(-12)color(red)(+16)# is the same as #ubrace(color(green)(-12)color(red)(+12))color(red)(+4)# # color(white)("ddddddd.ddddddddddddddd") darr # #color(white)("ddddddddddd.dddddddd.ddd")0color(white)("dd..")+4#