123. How can the following sentences be briefly recorded using mathematical symbols?
1) None of the numbers $a, b, c$ are equal to zero.
2) At least one of the numbers $a, b, c$ is equal to zero.
3) Either the numbers $a$ and $b$ have opposite signs, or at least one of them is equal to zero.
123. 124) $a b c \neq 0$; 2) $a b c=0$; 3) $a b \leqslant 0$.