:: deftheorem Def17 defines nor3 TWOSCOMP:def 17 :
for b₁ being Function of (3 -tuples_on BOOLEAN),BOOLEAN holds
( b₁ = nor3 iff for x, y, z being Element of BOOLEAN holds b₁ . <*x,y,z*> = 'not' ((x 'or' y) 'or' z) );