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IrredundantGeneratingSubset for a semigroup with a single repeated generator #160

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wilfwilson opened this issue Apr 22, 2016 · 1 comment
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IrredundantGeneratingSubset for a semigroup with a single repeated generator #160

wilfwilson opened this issue Apr 22, 2016 · 1 comment
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@wilfwilson
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In stable-2.7 and unstable 3.0, IrreundantGeneratingSubset first checks whether there is only one generator; and returns it if so. It then takes the set of generators (sorts and removes duplicates) and now continues, assuming there are at least 2 generators.

If the generating set consists of a single generator repeated multiple times, then this assumption is wrong and the function ends up failing, as below:

gap> S := Semigroup([Transformation([1, 1]), Transformation([1, 1])]);
<transformation semigroup of degree 2 with 2 generators>
gap> IrredundantGeneratingSubset(S);
Error, Usage: cannot create a semigroup with no generators, at /Users/Wilf/GAP/lib/semigrp.gi:570 called from
Semigroup( Difference( gens, [ x ] )

I'll submit a pull request to fix this.
@wilfwilson wilfwilson self-assigned this Apr 22, 2016
wilfwilson added a commit to wilfwilson/Semigroups that referenced this issue Apr 22, 2016
@wilfwilson
Fix IrredundantGeneratingSubset (Issue semigroups#160)
8c57afa 
IrreundantGeneratingSubset behaves incorrectly when given a
semigroup whose generating set consists of a single repeated
element.

Resolves: semigroups#160
wilfwilson added a commit to wilfwilson/Semigroups that referenced this issue Apr 22, 2016
@wilfwilson
Fix IrredundantGeneratingSubset (Issue semigroups#160)
3d9fdf3 
IrreundantGeneratingSubset behaves incorrectly when given a
semigroup whose generating set consists of a single repeated
element.

Resolves: semigroups#160
This was referenced Apr 22, 2016
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@wilfwilson wilfwilson added bug Label for issues or PR which report or fix bugs 3.0 and removed 3.0 labels Apr 22, 2016
james-d-mitchell added a commit that referenced this issue Apr 23, 2016
@james-d-mitchell
Merge pull request #162 from wilfwilson/fix-irredundant-stable-2.7
134682d 
Fix IrredundantGeneratingSubset in stable-2.7 (Issue #160)
james-d-mitchell added a commit that referenced this issue Apr 23, 2016
@james-d-mitchell
Merge pull request #161 from wilfwilson/fix-irredundant-unstable-3.0
b9e4341 
Fix IrredundantGeneratingSubset in unstable-3.0 (Issue #160)
@james-d-mitchell
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This is closed by PR #161 and #162

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@james-d-mitchell @wilfwilson