st: constraints in mlogit

["stata_user stata_user" <stata_dofile@hotmail.co.uk>]

Hi,
It is possible to test if two paramters are statistically equal in a mlogit?

Let Y a discrete variable with 3 categories y1 y2 y3

X1 continuous
X2 binary

I consider mlogit Y X1 X2

y1 is the reference

I obtain two paramters for each of X1 and X2 for the comparisons y2 vs y1 
and y3 vs y1

For example for X1:

let b21 be the parameter for the comparison y2 vs y1
let b31 be the parameter for the comparison y3 vs y1

How I can test H0: b21=b31

thanks

S.

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