| #### D.15.2.20 arrIsEssential Procedure from library `arr.lib` (see arr_lib). Usage: arrIsEssential(A); arrangement A; Return: boolean: 1 if arr is essential, i.e. rank of maximal element of poset is dimension Note: A has to be non-empty. Example:
    LIB "arr.lib";
    ring S = 0,(x,y,z),lp;
    arr A = ideal(x,y,z);
    arr B = ideal(x+y+z,x,y+z);
    arrIsEssential(A);
    ==> 1
    arrIsEssential(B);
    ==> 0
See also: arrCone; arrDecone; arrEssentialize; arrIsEssential; arrRestrict.

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