:: deftheorem Def10 defines field_by LATTICE4:def 11 :
for BL being Boolean Lattice
for A being non empty Subset of BL
for b₃ being Field of BL holds
( b₃ = field_by A iff ( A c= b₃ & ( for F being Field of BL st A c= F holds
b₃ c= F ) ) );