let Al be QC-alphabet ; :: thesis: for p being Element of CQC-WFF Al
for x being bound_QC-variable of Al
for A being non empty set
for J being interpretation of Al,A
for v being Element of Valuations_in (Al,A) holds
( J,v |= 'not' (Ex (x,('not' p))) iff J,v |= All (x,p) )
let p be Element of CQC-WFF Al; :: thesis: for x being bound_QC-variable of Al
for A being non empty set
for J being interpretation of Al,A
for v being Element of Valuations_in (Al,A) holds
( J,v |= 'not' (Ex (x,('not' p))) iff J,v |= All (x,p) )
let x be bound_QC-variable of Al; :: thesis: for A being non empty set
for J being interpretation of Al,A
for v being Element of Valuations_in (Al,A) holds
( J,v |= 'not' (Ex (x,('not' p))) iff J,v |= All (x,p) )
let A be non empty set ; :: thesis: for J being interpretation of Al,A
for v being Element of Valuations_in (Al,A) holds
( J,v |= 'not' (Ex (x,('not' p))) iff J,v |= All (x,p) )
let J be interpretation of Al,A; :: thesis: for v being Element of Valuations_in (Al,A) holds
( J,v |= 'not' (Ex (x,('not' p))) iff J,v |= All (x,p) )
let v be Element of Valuations_in (Al,A); :: thesis: ( J,v |= 'not' (Ex (x,('not' p))) iff J,v |= All (x,p) )
A1: ( not J,v |= Ex (x,('not' p)) iff for a being Element of A holds not J,v . (x | a) |= 'not' p ) by Th9;
A2: ( ( for a being Element of A holds not J,v . (x | a) |= 'not' p ) implies for a being Element of A holds J,v . (x | a) |= p )

proof

assume A3: for a being Element of A holds not J,v . (x | a) |= 'not' p ; :: thesis: for a being Element of A holds J,v . (x | a) |= p
let a be Element of A; :: thesis: J,v . (x | a) |= p
not J,v . (x | a) |= 'not' p by A3;
hence J,v . (x | a) |= p by VALUAT_1:17; :: thesis: verum

end;

( ( for a being Element of A holds J,v . (x | a) |= p ) implies for a being Element of A holds not J,v . (x | a) |= 'not' p ) by VALUAT_1:17;
hence ( J,v |= 'not' (Ex (x,('not' p))) iff J,v |= All (x,p) ) by A1, A2, SUBLEMMA:50, VALUAT_1:17; :: thesis: verum