Numerical Unanimity

Anchors a unanimity regarding a numerical value
The proof of unanimity is a transaction on the blockchain, emitted if and only if all declared signatories have signed a value close enough to the average signed value.
Let 
n be the number of signatories
a be the average signed value
d be the percentage of deviation toward a
S be the set of signed values. 
The unanimity is reached if:
∣S∣=n∧∀s in S,(1−d2)⋅a≤s≤(1+d2)⋅a|S|=n \land \forall s \space in \space S, (1-\frac d 2)·a ≤ s  ≤ (1+\frac d 2)·a∣S∣=n∧∀s in S,(1−2d​)⋅a≤s≤(1+2d​)⋅a
For example, say 2 signatories must sign a value with an authorized deviation of 2%. Unanimity is reached only in situation 2 below:
The unanimity logic is encoded by a smart contract that manages as many unanimity processes as necessary. 
The contract admin address creates a specification for a consensus with:
a unique consensus identifier
the list of required signatories
A signatory signs with:
the consensus id
the value
A “unanimity” transaction is generated when all signatories haves signed a quasi-equal value.
Below is the archetype implementation:
archetype unanimity
​
variable admin : role = @tz1ZXf37ZNfVupt5GVyrPJ76q8kbjFuD2z7R
​
asset sig identified by id signatory {
   id : string;
   signatory : address;
   value : int;
}
​
asset sig_spec {
   sid : string;
   signatories : list<address>;
   dev : int; /* deviation toward avg. in nb. of percent */
   expiration : date;
   signatures : partition<sig> = [];
} with {
   s0 : 0 <= dev <= 100;
}
​
entry create_sig (i : string, s : list<address>, d : int) {
   called by admin
   effect {
      sig_spec.add({ sid = i; signatories = s; dev = d; expiration = (now + 1d) });
   }
}
​
function get_signatures(spid : string) : list<address * int> {
   var l : list<address * int> = [];
   for s in sig_spec[spid].signatures do
      l := prepend(l, (sig[s].signatory, sig[s].value));
   done;
   return l
}
​
function check_sig_data(spid : string) : bool {
   var avg = sig_spec[spid].signatures.sum(value) / sig_spec[spid].signatures.count();
   var min = (1 - sig_spec[spid].dev / 200) * avg;
   var max = (1 + sig_spec[spid].dev / 200) * avg;
   var check = true;
   for s in sig_spec[spid].signatures do
      check &= min <= sig[s].value <= max
   done;
   return check
}
​
entry unanimity (spid : string, l : list<address * int>, d : int) {
   called by selfaddress
}
​
entry failed (spid : string, l : list<address * int>, d : int) {
   called by selfaddress
}
​
entry sign (spid : string, v : int) {
   require {
      r0 : contains(sig_spec[spid].signatories, caller);
   }
   effect {
      sig_spec[spid].signatures.add({spid; caller; v });
      if sig_spec[spid].signatures.count() = length (sig_spec[spid].signatories) then (
        var sigs = get_signatures(spid);
        var d = sig_spec[spid].dev;
        var selfentry = if check_sig_data (spid) then self.unanimity else self.failed;
        transfer 0tz to entry selfentry((spid, sigs, d));
        sig_spec.remove(spid);
      );
   }
}
​
entry clear_expired () {
   called by admin
   effect {
      sig_spec.select(the.expiration < now).clear();
   }
}
​
​
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