sage: P = Poset([list(range(12)),[[0, 1], [0, 2], [0, 4], [1, 3], [1, 5], [2, 3]
....: , [2, 9], [3, 11], [4, 5], [4, 6], [5, 8], [6, 7], [6, 9], [7, 8], [7, 10]
....: , [8, 11], [9, 10], [10, 11]]])
sage: libgap(P)
<A poset on 12 points>
sage: A = libgap(QQ).PosetAlgebra(P)
sage: S0 = A.SimpleModules()[0]
sage: cat = A.CatOfRightAlgebraModules()
sage: cp = cat.StalkComplex(S0, 0); cp
0 -> 0:(1,0,0,0,0,0,0,0,0,0,0,0) -> 0
sage: cp = cp.TauOfComplex();cp
0 -> 2: P8 -> 0
sage: cp = cp.TauOfComplex();cp
0 -> 3: P4 -> 2: P2 + P3 -> 1: P1 -> 0
sage: cp = cp.TauOfComplex();cp
0 -> 3: P12 -> 2: P4 -> 0
sage: cp = cp.TauOfComplex();cp
0 -> 2: P5 -> 0
sage: cp = cp.TauOfComplex();cp
0 -> 4: P12 -> 3: P4 + P9 + P10 -> 2: P2 + P3 + P7 -> 1: P1 -> 0
sage: cp = cp.TauOfComplex();cp
0 -> 3: P11 -> 0
sage: cp = cp.TauOfComplex();cp
0 -> 3: P2 -> 2: P1 -> 0
sage: cp = cp.TauOfComplex();cp
---------------------------------------------------------------------------
GAPError                                  Traceback (most recent call last)
<ipython-input-101-4faaf209ef21> in <module>()
----> 1 cp = cp.TauOfComplex();cp

/home/chapoton/sage3/local/lib/python3.7/site-packages/sage/libs/gap/element.pyx in sage.libs.gap.element.GapElement_MethodProxy.__call__ (build/cythonized/sage/libs/gap/element.c:20320)()
   2669             return GapElement_Function.__call__(self, * ([self.first_argument] + list(args)))
   2670         else:
-> 2671             return GapElement_Function.__call__(self, self.first_argument)
   2672 
   2673 

/home/chapoton/sage3/local/lib/python3.7/site-packages/sage/libs/gap/element.pyx in sage.libs.gap.element.GapElement_Function.__call__ (build/cythonized/sage/libs/gap/element.c:19265)()
   2515         try:
   2516             sig_GAP_Enter()
-> 2517             sig_on()
   2518             if n == 0:
   2519                 result = CALL_0ARGS(self.value)

GAPError: Error, List Element: <list>[1] must have an assigned value