CALL LCS("thisisatest", "testing123testing")
END

SUB LCS (a$, b$)
    IF LEN(a$) = 0 OR LEN(b$) = 0 THEN PRINT "": EXIT SUB
    WHILE LEN(b$)
        FOR j = LEN(b$) TO 1 STEP -1
            IF INSTR(a$, LEFT$(b$, j)) THEN PRINT LEFT$(b$, j): EXIT SUB
        NEXT j
        b$ = MID$(b$, 2)
    WEND
END SUB