function lcs(string a, b)
    integer la = length(a),
            lb = length(b),
        longest = 0
    string best = ""
    for i,ch in a do
        for j=1 to lb do
            if ch=b[j] then
                integer l=1
                while i+l<=la
                  and j+l<=lb
                  and a[i+l]=b[j+l] do
                    l += 1
                end while
                if l>longest then
                    longest = l
                    best = a[i..i+l-1]
                end if
            end if
        end for
    end for
    return best
end function
?lcs("thisisatest","testing123testing")
?lcs("testing123testing","thisisatest")