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 Th50:
  a '&' (b 'nand' c) = (a '&' 'not' b) 'or' (a '&' 'not' c)
proof
  thus a '&' (b 'nand' c) =a '&' 'not' (b '&' c) by th1
    .=a '&' ('not' b 'or' 'not' c) by BVFUNC_1:14
    .=(a '&' 'not' b) 'or' (a '&' 'not' c) by BVFUNC_1:12;
end;
