If I_m, n =∫_0^1 x^m -1 (1-x)^n -1 d x, for m, n ≥ 1, and ∫_0^1 (x^m -1 +x^n -1)/((1+x)^m + n) d x=α I_m, n, α ∈ R, then α equals \ \ \ \.

If $\displaystyle \mathrm{I}_{\mathrm{m}, \mathrm{n}}=\int_0^1 x^{\mathrm{m}-1}(1-x)^{\mathrm{n}-1} \mathrm{~d} x$, for $\displaystyle \mathrm{m}, \mathrm{n} \geqslant 1$, and $\displaystyle \int_0^1 \frac{x^{\mathrm{m}-1}+x^{\mathrm{n}-1}}{(1+x)^{\mathrm{m}+\mathrm{n}}} \mathrm{d} x=\alpha \mathrm{I}_{\mathrm{m}, \mathrm{n}}, \alpha \in \mathrm{R}$, then $\displaystyle \alpha$ equals \_\_\_\_.