NO
<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="cpfHTML.xsl"?>
<certificationProblem xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../xml/cpf.xsd">
<input>
 <trsInput>
  <trs>
   <rules>
    <rule>
     <lhs>
      <funapp>
       <name>a</name>
      </funapp>
     </lhs>
     <rhs>
      <funapp>
       <name>b</name>
      </funapp>
     </rhs>
    </rule>
    <rule>
     <lhs>
      <funapp>
       <name>a</name>
      </funapp>
     </lhs>
     <rhs>
      <funapp>
       <name>f</name>
       <arg>
        <funapp>
         <name>a</name>
        </funapp>
       </arg>
      </funapp>
     </rhs>
    </rule>
    <rule>
     <lhs>
      <funapp>
       <name>b</name>
      </funapp>
     </lhs>
     <rhs>
      <funapp>
       <name>f</name>
       <arg>
        <funapp>
         <name>f</name>
         <arg>
          <funapp>
           <name>b</name>
          </funapp>
         </arg>
        </funapp>
       </arg>
      </funapp>
     </rhs>
    </rule>
   </rules>
  </trs>
 </trsInput>
</input>
<cpfVersion>2.1</cpfVersion>
<proof>
 <crDisproof>
  <nonJoinableFork>
   <rewriteSequence>
    <startTerm>
     <funapp>
      <name>a</name>
     </funapp>
    </startTerm>
    <rewriteStep>
     <positionInTerm/>
     <rule>
      <lhs>
       <funapp>
        <name>a</name>
       </funapp>
      </lhs>
      <rhs>
       <funapp>
        <name>f</name>
        <arg>
         <funapp>
          <name>a</name>
         </funapp>
        </arg>
       </funapp>
      </rhs>
     </rule>
     <funapp>
      <name>f</name>
      <arg>
       <funapp>
        <name>a</name>
       </funapp>
      </arg>
     </funapp>
    </rewriteStep>
    <rewriteStep>
     <positionInTerm>
      <position>1</position>
     </positionInTerm>
     <rule>
      <lhs>
       <funapp>
        <name>a</name>
       </funapp>
      </lhs>
      <rhs>
       <funapp>
        <name>b</name>
       </funapp>
      </rhs>
     </rule>
     <funapp>
      <name>f</name>
      <arg>
       <funapp>
        <name>b</name>
       </funapp>
      </arg>
     </funapp>
    </rewriteStep>
   </rewriteSequence>
   <rewriteSequence>
    <startTerm>
     <funapp>
      <name>a</name>
     </funapp>
    </startTerm>
    <rewriteStep>
     <positionInTerm/>
     <rule>
      <lhs>
       <funapp>
        <name>a</name>
       </funapp>
      </lhs>
      <rhs>
       <funapp>
        <name>b</name>
       </funapp>
      </rhs>
     </rule>
     <funapp>
      <name>b</name>
     </funapp>
    </rewriteStep>
   </rewriteSequence>
   <usableRulesNonJoin>
    <differentInterpretation>
     <model>
      <finiteModel>
       <carrierSize>2</carrierSize>
       <interpret>
        <name>b</name>
        <arity>0</arity>
        <arithFunction>
         <natural>1</natural>
        </arithFunction>
       </interpret>
       <interpret>
        <name>f</name>
        <arity>1</arity>
        <arithFunction>
         <sum>
          <arithFunction>
           <natural>1</natural>
          </arithFunction>
          <arithFunction>
           <product>
            <arithFunction>
             <natural>1</natural>
            </arithFunction>
            <arithFunction>
             <variable>1</variable>
            </arithFunction>
           </product>
          </arithFunction>
         </sum>
        </arithFunction>
       </interpret>
      </finiteModel>
     </model>
    </differentInterpretation>
   </usableRulesNonJoin>
  </nonJoinableFork>
 </crDisproof>
</proof>
<origin>
 <proofOrigin>
  <tool>
   <name>ACP</name>
   <version>0.72</version>
  </tool>
 </proofOrigin>
</origin>
</certificationProblem>