let X be Subset of MC-wff; :: thesis: for p being Element of MC-wff holds (Nes p) => (Nes (Nes p)) in CnS4 X
let p be Element of MC-wff ; :: thesis: (Nes p) => (Nes (Nes p)) in CnS4 X
for T being Subset of MC-wff st T is S4_theory & X c= T holds
(Nes p) => (Nes (Nes p)) in T ;
hence (Nes p) => (Nes (Nes p)) in CnS4 X by Def23; :: thesis: verum