// This behaviour regularly increases the buying price.
TickerBehaviour adjustPriceBehaviour = ...;
// This method returns true if the ISBN is the one of the book to buy and the price
// is acceptable.
boolean isAcceptable(Constant isbn, Constant price) {...}

class PriceProposalSIP extends ApplicationSpecificSIPAdapter {
  public PriceProposalSIP() {
    super(BookBuyerCapabilities.this, "(B ??myself (selling_price ??isbn ??price ??seller))");
  }

  protected ArrayList doApply(MatchResult applyResult, ArrayList result, SemanticRepresentation sr) {
    final Constant isbn = (Constant)applyResult.term("isbn");
    final Constant price = (Constant)applyResult.term("price");
    if (isAcceptable(isbn, price)) {
      try {
        result.add(new SemanticRepresentation((Formula) SLPatternManip.instantiate(I_DONE_SELL_ACTION,
            "actor", applyResult.term("seller"),
            "isbn", isbn,
            "price", price,
            "buyer", getAgentName()))),
      }
      catch(Exception e) {e.printStackTrace();}
      // After committing to buy the book, the SIP becomes useless
      mySemanticInterpretationTable.removeSemanticInterpretationPrinciple(this);
    }
    return result;
  }
}