Step 1: In the notation of attributes, capital letters A, B, C denote presence, and the corresponding Greek letters denote absence. So \((\alpha B\gamma)\) is the class having B present but A and C absent.
Step 2: By inclusion-exclusion, \((B)\) (units with B present, regardless of A and C) must be reduced by the units that also carry A, i.e. \((AB)\), and by units that also carry C, i.e. \((BC)\). Units carrying B, A and C together, i.e. \((ABC)\), get removed twice in this process, so they are added back once.
Step 3: This gives the identity \[(\alpha B \gamma) = (B) - (AB) - (BC) + (ABC)\]
Step 4: This matches option (D) exactly.
\[\boxed{(\alpha B\gamma) = (B) - (AB) - (BC) + (ABC)}\]