PROC SUMMARY is 99% the same as PROC MEANS. The default outputs are different, SUMMARY defaults to output to a SAS data set, MEAN defaults to output as text in HTML or LISTING.
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Spaces wouldn't be an issue. The important bit is that it's within brackets for it to be syntax for a SAS dataset option. Without the brackets SAS will interpret it as an option for Proc Print - which doesn't exist to the code will fail.
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