[Cryptography] Quillon Graph

[Dennis Hamilton]

Viktor S. Kristensen wrote

     Definition 12.1 (Defense in Depth). Security requires breaking both classical and post-quantum components:

     Security = Sec(Classical) ∨ Sec(Post-Quantum)

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I don't have the document being discussed, but this formula strikes me as odd.  

Is Sec(x) taken to be a Boolean condition?   I assume the idea is that both must be compromised for a ciphertext at rest to be cracked.  But it's pretty absolute formulated as strictly true or false.

If Sec(x) is a probability, a different formulation is needed.  Something like

Vulnerability = (1 - Sec(Classical)) × (1 - Sec(Post-Quantum))

Security = 1 - Vulnerability

Working the same if Sec(x) is only 0 or 1.