HIMEM = PAGE + 200000000 : REM Increase recursion depth

      FOR k% = 0 TO 20
        PRINT FNA(k%, ^FN1(), ^FN_1(), ^FN_1(), ^FN1(), ^FN0())
      NEXT
      END

      DEF FNA(k%, x1%, x2%, x3%, x4%, x5%)
      IF k% <= 0 THEN = FN(x4%)(x4%) + FN(x5%)(x5%)
      LOCAL b{}
      DIM b{fn%, k%, x1%, x2%, x3%, x4%, x5%}
      b.fn% = !^FNB()
      b.k%  = k%
      b.x1% = x1%
      b.x2% = x2%
      b.x3% = x3%
      b.x4% = x4%
      b.x5% = x5%
      DEF FNB(!(^b{}+4))
      b.k% -= 1
      = FNA(b.k%, b{}, b.x1%, b.x2%, b.x3%, b.x4%)

      DEF FN0(d%) = 0
      DEF FN1(d%) = 1
      DEF FN_1(d%) = -1