RosettaCodeData/Task/Longest-common-substring/APL/longest-common-substring-1.apl

lcs←{
    sb←∪⊃,/{⌽¨,\⌽⍵}¨,\⍵
    match←(sb(∨/⍷)¨⊂⍺)/sb
    ⊃((⌈/=⊢)≢¨match)/match
}