Semantics Wording

I noticed in section 4.2

[[
RDFS Entailment Lemma. S rdfs-entails a graph E if and only if the
rdfs-closure of the merge of S with repect to the combined vocabulary of
S and E simply entails E.
]]

I had trouble parsing that - what is a merge with respect to a
vocabulary?  I can't figure out what this means so can't suggest an
alternative, but do suggest and intro phrase:

[[
A set of graphs S rdfs-entails ...
]]

Brian