On the structure of non-full-rank perfect q-ary codes

The Krotov combining construction of perfect 1-error-correcting binary codes from 2000 and a theorem of Heden saying that every non-full-rank perfect 1-errorcorrecting binary code can be constructed by this combining construction is generalized to the q-ary case. Simply, every non-full-rank perfect code C is the union of a well-defined family of μ̄-components Kμ̄, where μ̄ belongs to an “outer” perfect code C⋆, and these components are at distance three from each other. Components from distinct codes can thus freely be combined to obtain new perfect codes. The Phelps general product construction of perfect binary code from 1984 is generalized to obtain μ̄-components, and new lower bounds on the number of perfect 1-error-correcting q-ary codes are presented.