Bug in initialisation of species

[hivert]

The following specification is valid:

sage: Set0  = species.SetSpecies()
sage: Set1  = species.SetSpecies(min=1)
sage: Set2  = species.SetSpecies(min=2)
sage: Four = species.CombinatorialSpecies()
sage: Four.define(Set2(Four) + Set1*Set0(Four))

However, the following code breaks

sage: Four.generating_series()[1]
[...]
ValueError: generator already executing

Strangely enough, adding some seemingly unrelated instruction work
around it::

sage: Set0  = species.SetSpecies()
sage: Set1  = species.SetSpecies(min=1)
sage: Set2  = species.SetSpecies(min=2)

sage: Set2(Set1).generating_series()[1]
0

sage: Four = species.CombinatorialSpecies()
sage: Four.define(Set2(Four) + Set1*Set0(Four))
sage: Four.generating_series()[1]
1
sage: Four.generating_series()[4]
52/3
sage: Four.generating_series()
x + 2*x^2 + 16/3*x^3 + 52/3*x^4 + O(x^5)

Florent

CC: @sagetrac-sage-combinat @mantepse

Component: combinatorics

Keywords: Species, LazyPowerSeries

Issue created by migration from https://trac.sagemath.org/ticket/12649

[hivert]

comment:1

Here is a smaller code which triggers the problem:

Z     = species.SingletonSpecies()
Set2  = species.SetSpecies(min=2)
NMult   = species.CombinatorialSpecies()
NMult.define(Set2(Z+NMult))
NMult.generating_series()[0]

[mwhansen]

comment:3

Fixed in #15673.