# What is or could be the tag for asking about possibility of teaching certain topics without prerequisities?

For example, I had no idea that probabilities of 0 or 1 don't change with information. I don't recall being taught this in elementary or advanced probability. The advanced probability way of proving it would be with filtrations,

$$P(A|\mathscr F_t) = 1 \iff P(A|\mathscr F_s) =1 \iff P(A)= 1 \iff P(A|\mathscr G)= 1,$$

but there's a way without measure theory to prove a weaker result in elementary probability:

$$P(A|B) = 1 \iff P(A)=1$$

This needs no measure theory!

If I were unsure about the last statement or had no idea about the weaker result and were to ask something like 'How do I/Can I teach the concept that probabilities of 0 or 1 do not change when you add or remove conditions without measure theory?', what tag is or could be (is: it exists, so what is it? / could be: it doesn't exist, so what could be an appropriate tag?) appropriate?

• I don't think a special tag is needed. Just use some general tags like probability and prerequisites. – Joel Reyes Noche May 1 '18 at 10:46
• @JoelReyesNoche i said IS or could be. Prerequisites sounds right. Thanks ^-^ Happy 5th week of Easter – BCLC May 1 '18 at 10:50