In my first high school chemistry class, the teacher told everyone, "Water freezes at 0 degrees Celsius and ice melts at 0 degrees Celsius."
My instantaneous reaction was, "That's impossible!" Having studied science continuously since that first class, I now know that it truly is impossible. This is because of water's phase diagram. At the triple point, water, ice and steam all coexist at equilibrium. Water is not freezing and ice is not melting. It makes no sense to claim that putting a glass of water next to a glass of ice in a perfectly insulated container at 0 degrees Celsius and standard pressure, 760 mm of mercury, will cause the water to freeze and the ice
In fact, water is known to supercool down to 40 below zero (C or F, same temp) without freezing because it has to have a source of nucleation - something like a bacterium or speck of dust.