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Dear Gap - Forum,

I think there is a bug in BlistList :
if the second argument is a range, then you might get
a wrong result (see example).

Another problem concerning boolean lists :
if IsBlist recognizes a given list as a boolean list,
it will (at least) not necessary be converted to
compact Blist representation, contrary to the
description of the respective function in the
reference manual.
(At least if the results of SHALLOW_SIZE
are correct, see example).

Best regards,

Stefan Kohl

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gap> even := [4,6..20];
[ 4, 6 .. 20 ]
gap> l := BlistList([1..20],even);
[ false, false, false, true, true, true, true, true, true, true, true, true, 
  false, false, false, false, false, false, false, false ]  # serious nonsense, I think
gap> even[1] := 3;   # To convert the list from range representation
3                    # to 'ordinary' representation 
gap> even[1] := 4;
4
gap> even;
[ 4, 6, 8, 10, 12, 14, 16, 18, 20 ]
gap> l := BlistList([1..20],even);
[ false, false, false, true, false, true, false, true, false, true, false, 
  true, false, true, false, true, false, true, false, true ]  # correct, as expected



gap> b := List([1..1000],i->true);;
gap> SHALLOW_SIZE(b);
132
gap> b[1] := 0;
0
gap> SHALLOW_SIZE(b);
4004
gap> b[1] := false;
false
gap> SHALLOW_SIZE(b);
4004
gap> IsBlist(b);
true
gap> SHALLOW_SIZE(b);  # Why does GAP not convert b back
4004                   # to compact Blist representation ?

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