What do the numbers mean in the reasons section in proof sequences?

Question

Prove: p V q and not p => q

solution:

statements                Reasons
1. p V q                  Given
2. not p                  Given
3. not (not p) V q        Double Negation, 1
4. not p ->               implication, 3
5. q                      Modus Ponens, 4,2

Answer 1

They are references to earlier steps in the proof, which you can see have been numbered. For example:

3. not (not p) V q        Double Negation, 1

means that both Double Negation and step 1,

1. p V q                  Given

are being cited as reasons for statement 3 to be true.