Merge pull request #63 from zyklotomic/patch-1

Mention zero is neither postive nor negative in spec documentation

spec/v0-1.md

@@ -30,7 +30,7 @@ The mod operator `%` is a special case: `<e1>` and `<e2>` must evaluate to U64s.
 
 Arithmetic operations on two Nums yield Nums and are treated as field operations done modulo `p`; division is field division.
 
-Comparisons interpret Nums as signed. The first half ranging from `0` to `(p - 1)/2` is considered positive. The second half ranging from `(p - 1)/2 + 1` to `p - 1` is considered negative. For every positive `n`, there is a corresponding negative `m`, such that `n + m = 0`. The result is that the interpretation of signed Nums implied by the definition of < (etc.) is arithmetically consistent.
+Comparisons interpret Nums as signed. The first half ranging from `0` exclusive to `(p - 1)/2` is considered positive. The second half ranging from `(p - 1)/2 + 1` to `p - 1` is considered negative. For every positive `n`, there is a corresponding negative `m`, such that `n + m = 0`. Furthermore, `0` is considered neither positive nor negative, and we have that `0 + 0 = 0`. The result is that the interpretation of signed Nums implied by the definition of < (etc.) is arithmetically consistent.
 
 Arithmetic operations on two U64s yield U64s and are done modulo `2^64`; divison is integer division.