Correct the derivation of a Sapling child full viewing key's nk, and …

…define the bases G and H.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

zip-0032.rst

@@ -181,6 +181,8 @@ CDKsk((*ask*\ :sub:`par`\ , *nsk*\ :sub:`par`\ , *ovk*\ :sub:`par`\ , *dk*\ :sub
 
 Deriving a child extended full viewing key
 ``````````````````````````````````````````
+Let 𝓖 be as defined in [#sapling-spec]_ section 5.4.6.1 and let 𝓗 be as defined in [#sapling-key-components]_.
+
 CDKfvk((*ak*\ :sub:`par`\ , *nk*\ :sub:`par`\ , *ovk*\ :sub:`par`\ , *dk*\ :sub:`par`\ , *c*\ :sub:`par`\ ), *i*) →
 (*ak*\ :sub:`i`\ , *nk*\ :sub:`i`\ , *ovk*\ :sub:`i`\ , *dk*\ :sub:`i`\ , *c*\ :sub:`i`\ )
 
@@ -194,8 +196,8 @@ CDKfvk((*ak*\ :sub:`par`\ , *nk*\ :sub:`par`\ , *ovk*\ :sub:`par`\ , *dk*\ :sub:
 - Let *I*\ :sub:`nsk` = ToScalar(PRF\ :sup:`expand`\ (*I*\ :sub:`L`\ , [0x14]))
 - Return:
 
-  - *ak*\ :sub:`i` = [*I*\ :sub:`ask`\ ] *G* + *ak*\ :sub:`par`
-  - *nk*\ :sub:`i` = [*I*\ :sub:`nsk`\ ] *G* + *nk*\ :sub:`par`
+  - *ak*\ :sub:`i` = [*I*\ :sub:`ask`\ ] 𝓖 + *ak*\ :sub:`par`
+  - *nk*\ :sub:`i` = [*I*\ :sub:`nsk`\ ] 𝓗 + *nk*\ :sub:`par`
   - *ovk*\ :sub:`i` = truncate\ :sub:`32`\ (PRF\ :sup:`expand`\ (*I*\ :sub:`L`\ , [0x15] || *ovk*\ :sub:`par`\ ))
   - *dk*\ :sub:`i` = truncate\ :sub:`32`\ (PRF\ :sup:`expand`\ (*I*\ :sub:`L`\ , [0x16] || *dk*\ :sub:`par`\ ))
   - *c*\ :sub:`i` = *I*\ :sub:`R`