st: Substituting submatrix

[Rachel <academicgirl@gmail.com>]

How can one efficiently replace a submatrix in Stata?  For example,
suppose we have C, an 6x6 identity matrix and would like to subsitute
[3,4\5,6]  as the upper left 2x2 submatrix.

I've tried mat C[1..2,1..2]=3,4\5,6

but this leads to a syntax error.

Thanks,
Rachel
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