In order to analyze gender wage gap, the following is conducted.
However, It is impossible to proceed because of the "oaxaca already defined"
Who can help me with this problem?

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xi: rifreg lnwage age whour i.edu i.union i.married i.fsize tenure if gender==0, quantile(0.5) w(0.06) retain(rif_m50)
estimates store male_wage
xi: rifreg lnwage age whour i.edu i.union i.married i.fsize tenure if gender==1, quantile(0.5) w(0.06) retain(rif_f50)
estimates store female_wage
oaxaca8 male_wage female_wage
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oaxaca already defined
(error occurred while loading oaxaca8.ado)