procedure lcs(s1,s2)  # return longest common substring of s1 and s2
    if *s1 > *s2 then s1 :=: s2             # s1 is the shorter string
    return s1 ? if j := *s1 to 1 by -1 &    # Return substring, s, of s1 that is
                   tab(1 to *s1) &          # also a substring of s2. Evaluate s from
                   find(s := move(j),s2)  then s else ""    # longest to shortest.
end

procedure main(A)
    lcstest("thisisatest","testing123testing")
    lcstest("abracadabra","arabracae")
    lcstest("abc","123")
    lcstest("testing","sting")
    lcstest("thisisatest_stinger","testing123testingthing")
    lcstest("thisisatest_stinger","thisis")
    lcstest("testing123testingthing","thisis")
    lcstest("thisisatest","thisisatest")
end

procedure lcstest(s1,s2)
    write("\"",s1,"\" and ","\"",s2,"\" --> \"",lcs(s1,s2),"\"")
end