Problem using unit "mn"

[parisse]

I speak for CAS, USIMPLIFY is not a CAS command.
usimplify(1_mn) returns 60_s.
usimplify(1_min) will return 60_s.
You can make most of the time the distinction between CAS and Home with lowercase vs uppercase commands. In doubt, try to type the commandname alone : usimplify alone or USIMPLIFY alone. A CAS command is an object, a Home command is not, it will error.