:: deftheorem SymDist defines SymmetricDiffDist ROUGHIF2:def 11 :
for X being finite set
for b₂ being Function of [:(bool X),(bool X):],REAL holds
( b₂ = SymmetricDiffDist X iff for x, y being Subset of X holds b₂ . (x,y) = card (x \+\ y) );