function offerTkn(uint _tokensOffered, uint _tokenPrice) public {
        require(_humanSender(msg.sender));
        require(tknAddrNdx[msg.sender] == 0); 
        require(0 < _tokensOffered); 
        require(phxCoin.transferFrom(msg.sender, this, _tokensOffered)); 
        tknTokensOffered[msg.sender] = _tokensOffered;
        tknPricePerToken[msg.sender] = _tokenPrice; 
        tknOfferors.push(msg.sender);
        tknAddrNdx[msg.sender] = tknOfferors.length - 1;
    }