reserve Y for non empty set,
  a,b,c,d for Function of Y,BOOLEAN;
reserve Y for non empty set,
  a,b,c for Function of Y,BOOLEAN;

theorem Th35:
  a 'nor' (b 'eqv' c) = ('not' a) '&' (b 'xor' c)
proof
  thus a 'nor' (b 'eqv' c) = 'not' (a 'or' (b 'eqv' c)) by Th2
    .= ('not' a) '&' ('not' (b 'eqv' c)) by BVFUNC_1:13
    .= ('not' a) '&' ('not' 'not' (b 'xor' c)) by Th12
    .= ('not' a) '&' (b 'xor' c);
end;
