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Clear stored inverse when calling TrimPerm
This is required if TrimPerm changes the TNUM of the permutation, as a permutation and its stored inverse must have the same TNUM. This is also required if TrimPerm changes the permutation (although this would break many other things if anyone did it)
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# When TRIM_PERM causes a permutation 'p' to change TNAM, the stored inverse | ||
# must be cleared, as the stored inverse of 'p' must have the | ||
# same TNAM as 'p' | ||
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# Make p a Perm4 | ||
gap> p := (1,2,3,4)*(2^16,2^16+1)*(2^16,2^16+1); | ||
(1,2,3,4) | ||
gap> IsPerm4Rep(p); | ||
true | ||
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# Force inverse calculation | ||
gap> q := p^-1; | ||
(1,4,3,2) | ||
gap> IsPerm4Rep(q); | ||
true | ||
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# Now trim | ||
gap> TRIM_PERM(p, 4); | ||
gap> IsPerm2Rep(p); | ||
true | ||
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# Check inverse is also a perm2 | ||
gap> IsPerm2Rep(p^-1); | ||
true | ||
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# But this has not changed q | ||
gap> IsPerm4Rep(q); | ||
true | ||
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# and it's inverse is the correct type | ||
gap> IsPerm4Rep(q^-1); | ||
true | ||
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# Check some calculations that use the inverse | ||
gap> List([1..5], x -> x/p); | ||
[ 4, 1, 2, 3, 5 ] | ||
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# And on q (to ensure it's inverse is not still 'p') | ||
gap> List([1..5], x -> x/q); | ||
[ 2, 3, 4, 1, 5 ] |