st: Follow up on matrix building question

[Kerem Yaman <kerem@yamans.com>]

With the help from the list I can now get to the point
where I have a matrix A that looks like this:
A[3,3]
     coffee  sugar  wheat
coffee     1     1     2
coffee     2     2     1
> r3     0     0     2
> 
> A[3,3]

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