A finite presentation of F is given by the following expression:

${\displaystyle \langle A,B\mid \ [AB^{-1},A^{-1}BA]=[AB^{-1},A^{-2}BA^{2}]=\mathrm {id} \rangle }$ 

where [x,y] is the usual group theory commutator, xyx⁻¹y⁻¹.

Although F has a finite presentation with 2 generators and 2 relations, it is most easily and intuitively described by the infinite presentation:

${\displaystyle \langle x_{0},x_{1},x_{2},\dots \ \mid \ x_{k}^{-1}x_{n}x_{k}=x_{n+1}\ \mathrm {for} \ k<n\rangle .}$ 

The two presentations are related by x₀=A, x_n = A¹⁻ⁿBAⁿ⁻¹ for n>0.

The group F also has realizations in terms of operations on ordered rooted binary trees, and as a subgroup of the piecewise linear homeomorphisms of the unit interval that preserve orientation and whose non-differentiable points are dyadic rationals and whose slopes are all powers of 2.

The group F can also be considered as acting on the unit circle by identifying the two endpoints of the unit interval, and the group T is then the group of automorphisms of the unit circle obtained by adding the homeomorphism x→x+1/2 mod 1 to F. On binary trees this corresponds to exchanging the two trees below the root. The group V is obtained from T by adding the discontinuous map that fixes the points of the half-open interval [0,1/2) and exchanges [1/2,3/4) and [3/4,1) in the obvious way. On binary trees this corresponds to exchanging the two trees below the right-hand descendant of the root (if it exists).

The Thompson group F is the group of order-preserving automorphisms of the free Jónsson–Tarski algebra on one generator.

The conjecture of Thompson that F is not amenable was further popularized by R. Geoghegan—see also the Cannon–Floyd–Parry article cited in the references below. Its current status is open: E. Shavgulidze^[1] published a paper in 2009 in which he claimed to prove that F is amenable, but an error was found, as is explained in the MR review.

It is known that F is not elementary amenable, see Theorem 4.10 in Cannon–Floyd–Parry.

If F is not amenable, then it would be another counterexample to the now disproved von Neumann conjecture for finitely-presented groups, which states that a finitely-presented group is amenable if and only if it does not contain a copy of the free group of rank 2.

The group F was rediscovered at least twice by topologists during the 1970s. In a paper that was only published much later but was in circulation as a preprint at that time, P. Freyd and A. Heller ^[2] showed that the shift map on F induces an unsplittable homotopy idempotent on the Eilenberg–MacLane space K(F,1) and that this is universal in an interesting sense. This is explained in detail in Geoghegan's book (see references below). Independently, J. Dydak and P. Minc ^[3] created a less well-known model of F in connection with a problem in shape theory.

In 1979, R. Geoghegan made four conjectures about F: (1) F has type FP_∞; (2) All homotopy groups of F at infinity are trivial; (3) F has no non-abelian free subgroups; (4) F is non-amenable. (1) was proved by K. S. Brown and R. Geoghegan in a strong form: there is a K(F,1) with two cells in each positive dimension.^[4] (2) was also proved by Brown and Geoghegan ^[5] in the sense that the cohomology H*(F,ZF) was shown to be trivial; since a previous theorem of M. Mihalik ^[6] implies that F is simply connected at infinity, and the stated result implies that all homology at infinity vanishes, the claim about homotopy groups follows. (3) was proved by M. Brin and C. Squier.^[7] The status of (4) is discussed above.

It is unknown if F satisfies the Farrell–Jones conjecture. It is even unknown if the Whitehead group of F (see Whitehead torsion) or the projective class group of F (see Wall's finiteness obstruction) is trivial, though it easily shown that F satisfies the strong Bass conjecture.

D. Farley ^[8] has shown that F acts as deck transformations on a locally finite CAT(0) cubical complex (necessarily of infinite dimension). A consequence is that F satisfies the Baum–Connes conjecture.

• Higman group
• Non-commutative cryptography

• Cannon, J. W.; Floyd, W. J.; Parry, W. R. (1996), "Introductory notes on Richard Thompson's groups" (PDF), L'Enseignement Mathématique, IIe Série, 42 (3): 215–256, ISSN 0013-8584, MR 1426438
• Cannon, J.W.; Floyd, W.J. (September 2011). "WHAT IS...Thompson's Group?" (PDF). Notices of the American Mathematical Society. 58 (8): 1112–1113. ISSN 0002-9920. Retrieved December 27, 2011.
• Geoghegan, Ross (2008), Topological Methods in Group Theory, Graduate Texts in Mathematics, vol. 243, Springer Verlag, arXiv:math/0601683, doi:10.1142/S0129167X07004072, ISBN 978-0-387-74611-1, MR 2325352
• Higman, Graham (1974), Finitely presented infinite simple groups, Notes on Pure Mathematics, vol. 8, Department of Pure Mathematics, Department of Mathematics, I.A.S. Australian National University, Canberra, ISBN 978-0-7081-0300-5, MR 0376874