(For In[1] see Setup)
Symmetry Type
In[2]:=

?SymmetryType

SymmetryType[K] returns the symmetry type of the knot K, if known to KnotTheory`. The possible types are: Reversible, FullyAmphicheiral, NegativeAmphicheiral and Chiral.


In[3]:=

SymmetryType::about

The symmetry type data known to KnotTheory` is taken from Charles Livingston's "Table of Knot Invariants", http://www.indiana.edu/~knotinfo/.


The inverse of a knot is the knot obtained from it by reversing its parametrization. The mirror of A knot is obtained from by reversing the orientation of the ambient space, or, alternatively, by flipping all the crossings of .
A knot is called "fully amphicheiral" if it is equal to its inverse and also to its mirror. The first knot with this property is
In[4]:=

Select[AllKnots[],
(SymmetryType[#] == FullyAmphicheiral) &, 1]

Out[4]=

{Knot[4, 1]}

A knot is called "reversible" if it is equal to its inverse yet it different from its mirror (and hence also from the inverse of its mirror). Many knots have this property; indeed, the first one is:
In[5]:=

Select[AllKnots[],
(SymmetryType[#] == Reversible) &, 1]

Out[5]=

{Knot[3, 1]}

A knot is called "positive amphicheiral" if it is different from its inverse but equal to its mirror. There are no such knots with up to 11 crossings.
A knot is called "negative amphicheiral" if it is different from its inverse and its mirror, yet it is equal to the inverse of its mirror. The first knot with this property is
In[6]:=

Select[AllKnots[],
(SymmetryType[#] == NegativeAmphicheiral) &, 1]

Out[6]=

{Knot[8, 17]}

Finally, if a knot is different from its inverse, its mirror and from the inverse of its mirror, it is "chiral". The first such knot is
In[7]:=

Select[AllKnots[],
(SymmetryType[#] == Chiral) &, 1]

Out[7]=

{Knot[9, 32]}

It is a amusing to take "symmetry type" statistics on all the prime knots with up to 11 crossings:
In[8]:=

Plus @@ (SymmetryType /@ Rest[AllKnots[]])

Out[8]=

216 Chiral + 13 FullyAmphicheiral + 7 NegativeAmphicheiral +
565 Reversible

Unknotting Number
The unknotting number of a knot is the minimal number of crossing changes needed in order to unknot .
In[9]:=

?UnknottingNumber

UnknottingNumber[K] returns the unknotting number of the knot K, if known to KnotTheory`. If only a range of possible values is known, a list of the form {min, max} is returned.


In[10]:=

UnknottingNumber::about

The unknotting numbers of torus knots are due to ???. All other unknotting numbers known to KnotTheory` are taken from Charles Livingston's "Table of Knot Invariants", http://www.indiana.edu/~knotinfo/.


Of the 512 knots whose unknotting number is known to KnotTheory`
, 197 have unknotting number 1, 247 have unknotting number 2, 54 have unknotting number 3, 12 have unknotting number 4 and 1 has unknotting number 5:
In[11]:=

Plus @@ u /@ Cases[UnknottingNumber /@ AllKnots[], _Integer]

Out[11]=

u[0] + 197 u[1] + 247 u[2] + 54 u[3] + 12 u[4] + u[5]

There are 4 knots with up to 9 crossings whose unknotting number is unknown:
In[12]:=

Select[AllKnots[],
Crossings[#] <= 9 && Head[UnknottingNumber[#]] === List &
]

Out[12]=

{Knot[9, 10], Knot[9, 13], Knot[9, 35], Knot[9, 38]}

3Genus
A Seifert surface for a knot is a compact oriented surface
with boundary . Seifert surfaces exist, but are not unique. The SeifertView programme is a visual implementation of the algorithm of Seifert (1934) for
the construction of a Seifert surface from a knot projection. The 3genus of a knot is the minimal genus of a
Seifert surface for that knot.
In[13]:=

?ThreeGenus

ThreeGenus[K] returns the 3genus of the knot K or a list of the form {lower bound, upper bound}.


In[14]:=

ThreeGenus::about

The 3genus program was written by Jake Rasmussen of Princeton University. The program tries to compute the highest nonvanishing group in the knot Floer homology, using Ozsvath and Szabo's version of the Kauffman state model.


The highest 3genus of the knots known to KnotTheory` is , and there is only one knot with up to 11 crossings whose 3genus is 5:
In[15]:=

Max[ThreeGenus /@ AllKnots[]]

Out[15]=

5

In[16]:=

Select[AllKnots[], ThreeGenus[#] == 5 &]

Out[16]=

{Knot[11, Alternating, 367]}

(K11a367 is, of couse, also known as the torus knot T(11,2)).
The Conway knot K11n34 is the closure of the braid BR[4, {1, 1, 2, 3, 2, 1, 3, 2, 2, 3, 3}]. Let us compute its 3genus and compare it with the 3genus of its mutant companion, the KinoshitaTerasaka knot K11n42:
In[17]:=

ThreeGenus[BR[4, {1, 1, 2, 3, 2, 1, 3, 2, 2, 3, 3}]]

Out[17]=

3

In[18]:=

ThreeGenus[Knot[11, NonAlternating, 42]]

Out[18]=

2

Bridge Index
The bridge index' of a knot is the minimal number of local maxima (or local minima) in a generic smooth embedding of in .
In[19]:=

?BridgeIndex

BridgeIndex[K] returns the bridge index of the knot K, if known to KnotTheory`.


In[20]:=

BridgeIndex::about

The bridge index data known to KnotTheory` is taken from Charles Livingston's "Table of Knot Invariants", http://www.indiana.edu/~knotinfo/.


An often studied class of knots is the class of 2bridge knots, knots whose bridge index is 2. Of the 49 prime 9crossings knots, 24 are 2bridge:
In[21]:=

Select[AllKnots[], Crossings[#] == 9 && BridgeIndex[#] == 2 &]

Out[21]=

{Knot[9, 1], Knot[9, 2], Knot[9, 3], Knot[9, 4], Knot[9, 5],
Knot[9, 6], Knot[9, 7], Knot[9, 8], Knot[9, 9], Knot[9, 10],
Knot[9, 11], Knot[9, 12], Knot[9, 13], Knot[9, 14], Knot[9, 15],
Knot[9, 17], Knot[9, 18], Knot[9, 19], Knot[9, 20], Knot[9, 21],
Knot[9, 23], Knot[9, 26], Knot[9, 27], Knot[9, 31]}

Super Bridge Index
The super bridge index of a knot is the minimal number, in a generic smooth embedding of in , of the maximal number of local maxima (or local minima) in a rigid rotation of that projection.
In[22]:=

?SuperBridgeIndex

SuperBridgeIndex[K] returns the super bridge index of the knot K, if known to KnotTheory`. If only a range of possible values is known, a list of the form {min, max} is returned.


In[23]:=

SuperBridgeIndex::about

The super bridge index data known to KnotTheory` is taken from Charles Livingston's "Table of Knot Invariants", http://www.indiana.edu/~knotinfo/.


Nakanishi Index
In[24]:=

?NakanishiIndex

NakanishiIndex[K] returns the Nakanishi index of the knot K, if known to KnotTheory`.


In[25]:=

NakanishiIndex::about

The Nakanishi index data known to KnotTheory` is taken from Charles Livingston's "Table of Knot Invariants", http://www.indiana.edu/~knotinfo/.


Synthesis
In[26]:=

Profile[K_] := Profile[
SymmetryType[K], UnknottingNumber[K], ThreeGenus[K],
BridgeIndex[K], SuperBridgeIndex[K], NakanishiIndex[K]
]

In[27]:=

Profile[Knot[9,24]]

Out[27]=

Profile[Reversible, 1, 3, 3, {4, 6}, 1]

In[28]:=

Ks = Select[AllKnots[], (Crossings[#] == 9 && Profile[#]==Profile[Knot[9,24]])&]

Out[28]=

{Knot[9, 24], Knot[9, 28], Knot[9, 30], Knot[9, 34]}

In[29]:=

Alexander[#][t]& /@ Ks

Out[29]=

3 5 10 2 3
{13  t +     10 t + 5 t  t ,
2 t
t
3 5 12 2 3
15 + t   +  + 12 t  5 t + t ,
2 t
t
3 5 12 2 3
17  t +     12 t + 5 t  t ,
2 t
t
3 6 16 2 3
23  t +     16 t + 6 t  t }
2 t
t
