ABCI spec has inconsistencies regarding when PrepareProposal and ProcessProposal are called.
Specifically, in the "Overview and basic concepts" section, it is stated that both are called only if a process hasn't locked on a value, while in the "Methods" section, the conditions are different:

1. For PrepareProposal, a valid value is consulted instead (valid value != nil doesn't necessarily mean that locked value is != nil).

2. For ProcessProposal, it is written that it is called whenever a process should send a Prevote message (notice that this can happen even when the process has locked value != nil, [arXiv paper line 30]).

Spec should be fixed to match what is written in "Overview and basic concepts".
In addition, a file explaining why a process doesn't need to call PrepareProposal and ProcessProposal if it has a locked value != nil should be added.