Fixes an extra occurrence of "set of partial functions"

Author: Tpt

spec/index.html

@@ -9530,8 +9530,8 @@ <h4>Aggregate Algebra</h4>
             <div id="defn_algGroup">
               <b>Definition: Group</b>
             </div>
-            <p>Group evaluates a list of expressions against a solution sequence Ψ, producing a set
-              of partial functions from keys to solution sequences.</p>
+            <p>Group evaluates a list of expressions against a solution sequence Ψ, producing a
+              partial function from keys to solution sequences.</p>
             <p>Group(exprlist, Ψ) = { ListEval(exprlist, μ) → [ μ' | μ' in Ψ, ListEval(exprlist, μ)
               = ListEval(exprlist, μ') ] | μ in Ψ }</p>
           </div>