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checks if a facet complex is a tree
IsTree5(L: LIST): [BOOL, LIST ]
IsTree5(L: LIST, "NOOPT"): [BOOL, LIST]
IsTree5(L: LIST, "OPT"): [BOOL, LIST]
IsTree5(L: LIST, "CS_NOOPT"): [BOOL, LIST]
IsTree5(L: LIST, "CS_OPT"): [BOOL, LIST]

***** NOT YET IMPLEMENTED *****
This function is implemented in CoCoALib.
This function tests whether the facet complex described by the
list L of square free power products is a tree, plus a list which:
 is empty if L is a tree
 contains three elements of a cycle of L if L is not a tree.
Four options
NOOPT
,
OPT
,
CS_NOOPT
,
CS_OPT
are available as second
argument, specifying different algorithms; the default is
CS_OPT
.
For a full description of the algorithms we refer to the paper by
M. Caboara, S. Faridi, and P. Selinger, "Simplicial cycles and
the computation of simplicial trees", Journal of Symbolic Computation,
vol.42/12, pp.7788 (2006).
Use R ::= QQ[x,y,z,t];
D := [x*y, y*z, z*t, t*x];
IsTree5(D);
[False, [xy, xt, yt]]

IsTree5([xy, yz, zt]);
[True, [ ]]

