function lcs(sequence a, b)
sequence res = ""
    if length(a) and length(b) then
        if a[$]=b[$] then
            res = lcs(a[1..-2],b[1..-2])&a[$]
        else
            sequence l = lcs(a,b[1..-2]),
                     r = lcs(a[1..-2],b)
            res = iff(length(l)>length(r)?l:r)
        end if
    end if
    return res
end function

constant tests = {{"1234","1224533324"},
                  {"thisisatest","testing123testing"}}
for i=1 to length(tests) do
    string {a,b} = tests[i]
    ?lcs(a,b)
end for