Explanation by example
File "a"
abc
123
cfg
12345
fghh
1aaaaa


file "b"
ssssss
ffff
33
123
gggggkl
ffggg
1aaaaa

file "c" shoud read
ssssss
ffff
33
abc ----- note this inserted because "123" found in files "A","B"
123
gggggkl
ffggg
fghh ---- note this inserted because 1aaaaa found in files "A","B"
1aaaaa
Thanx
Smbs