 The logico-mathematical fact behind this is the difference in logical powers between “All” and “Almost all”. If all \(A\)-worlds are \(B\)-worlds (and there are some \(C \amp A\)-worlds) then all \(C \amp A\)-worlds are \(B\)-worlds. But we can have: almost all \(A\)-worlds are \(B\)-worlds but no \(C \amp A\)-world is a \(B\)-world. If all \(A\)-worlds are \(B\)-worlds and all \(B\)-worlds are \(C\)-worlds, then all \(A\)-worlds are \(C\)-worlds. But we can have: all \(A\)-worlds are \(B\)-worlds, almost all \(B\)-worlds are \(C\)-worlds, yet no \(A\)-world is a \(C\)-world; just as we can have, all kiwis are birds, almost all birds fly, but no kiwi flies.