code: public Constant oppositeConstant(String fldName) {
  		if (lhs.isFieldName() && lhs.asFieldName().equals(fldName)
  				&& rhs.isConstant())
  			return rhs.asConstant();
  		if (rhs.isFieldName() && rhs.asFieldName().equals(fldName)
  				&& lhs.isConstant())
  			return lhs.asConstant();
  		return null;
  	}
docs: Determines if this term is of the form "F&lt;OP&gt;C" where F is the
  specified field, &lt;OP&gt; is an operator, and C is some constant. If
  so, the method returns C. If not, the method returns null.
  
  @param fldName
  the name of the field
  @return either the constant or null