Meaning of colon in group theory, if not subgroup index?

[AgentBased]

I am reading a paper where the author uses colons in the description of groups. Example (not verbatim): "This subgroup is isomorphic to (Z_5 X A_4):Z_2". Several subgroups are described in the same way (as (G_1 x G_2):G_3) throughout the paper.

I have seen the colon in G to indicate the index of a subgroup H, in G, but that doesn't seem to make sense in this context. Does anyone know what this means?

 

[Landau]

Perhaps /, as in quotient group G/H? (they both suggest some sort of division)

 

[AgentBased]

Evidently, it turns out that it's semi-direct product. The notation comes from the computational algebra system GAP.