st: Spotting changes in identifier

["Pavlos C. Symeou" <p.symeou@lmu.de>]

I have panel data on a number of companies over a series of years. 
Two of my variables uniquely identify an observation (Name and 
Ticker). For different reasons:
a) the Name may have changed over the years whilst the Ticker may 
have remained the same;
year      name   ticker
1999    stata   ss
2000    strata ss

b) the Ticker may have changed over the years whilst Name may have 
remained the same;
year      name   ticker
1999    stata   ss
2000    stata   sss

c) both may have changed

year      name   ticker
1999    stata   ss
2000    strata sss


I am interested in identifying cases a) and b) above (considering 
that case c might require visual observation rather than an 
automated process)
Do you have any suggestions?

I have tried

bysort name: l name ticker year if ticker[_n]!="ticker[_n+1]"

but it doesn't seem to work. Both Name and Ticker are string variables.

Best,

Pavlos
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