The F4 generation is the first generation that can be a "stud book tradition" (SBT) cat and is considered "purebred". A Savannah cross may also be referred to by breeders as "SV × SV" (where SV is the TICA code for the Savannah breed). Savannah generation filial numbers also have a letter designator that refers to the generation of SV-to-SV breeding. The designation A means one parent is a Savannah and the other is an outcross. B is used when both parents are Savannahs, with one of them being an A. The C designation is used when both parents are Savannahs and one of them is a B. Therefore, A × (any SV) = B; B × (B,C,SBT) = C; C × (C, SBT) = SBT, SBT × SBT = SBT. F1 generation Savannahs are always A, since the father is a nondomestic outcross (the serval father). The F2 generation can be A or B. The F3 generation can be A, B or C. SBT cats arise in the F4 generation.