Thread: Is it necessary to prove this or is it redundant

1. Is it necessary to prove this or is it redundant

Hi,

this post is connected to How to prove it post. Since then i have been reading about how to use proofs but am still a newbie in the area. so my question to you guys is: Is this relevant to be proven or am i just wasting my time?

What I have is an array A of numbers. Every number in this array has an index. the indexes span from 0 to n. initial boundary conditions that are given are:

1. $i \in n$ is index and $0 \leq i \leq n$
2. $A[i]$ is a value, a number in array A at position i and $0 \leq A[i] \leq n - i$

Is is necessary to prove:

Prove that for every $0 \leq i \leq n - A[i]$ there exists $j \in n$ such that $j - A[i] = i$.

or is this totally redundant and obvious form the initial conditions since all i need to do is to plug-in the expression for j and show that it equals to i (of course if this is the correct way to prove this ).

thank you

Baxy

PS

Also what confuses me is this $0 \leq i \leq n - A[i]$ condition. Do i need some how show that if this condition isn't met then $j > n$ can appear ??

2. Re: Is it necessary to prove this or is it redundant

What do you mean by $j \in n$?

3. Re: Is it necessary to prove this or is it redundant

well yes this is wrong it should be

$0\leq j \leq n$

but this i somehow passed , or at least i think i did. i posted the solution that does not include the above example since i decided it was redundant i the Please help: proof involvim array elements :CS post. thanx