V. Keränen, Abelian squares are avoidable on 4 letters, Proc. ICALP '92, Lecture Notes in Comp. Sci. 623, Springer, Berlin (1992), pp. 41–52

Keränen's infinite word is given as the fixed point of a 85-uniform morphism g₈₅ defined by:

g₈₅(a)=abcacdcbcdcadcdbdabacabadbabcbdbcbacbcdcacbabdabacadcbcdcacdbcbacbcd
          cacdcbdcdadbdcbca

g₈₅(b)=σ(h(a))

g₈₅(c)=σ²(h(a))

g₈₅(d)=σ³(h(a))

where σ is a cyclic permutation of letters:

σ: a ↦ b, b ↦ c, c ↦ d, d ↦ a

-- StepanHolub - 10 Mar 2012