Mathcad 2000 has that feature - for collapsing an area, hiding it from view, and even password-protecting it. In MCAD 2000 first you click a blank region in the MCAD document then do an 'Insert/Area' from the Insert Menu. Then you do 'Format/Area' from the Format drop-down menu.
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Whiskey, women -- and astrophysics. Because sometimes a problem can't be solved with just whiskey and women.
I know. That is why I mentioned it, thinking that there was maybe a language mistranslation. Just trying to get at the real problem (which you must admit can be somewhat elusive here).
"Unit" may = "area" in OP's translation.
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"Reason is not automatic. Those who deny it cannot be conquered by it. Do not count on them. Leave them alone." - Ayn Rand