Can only be minted in exchange for RBTC. Given an amount of RBTC paid to the contract, the system calculates the corresponding BitPro amount to mint, RBTC and Bitpro balances are added to the base bucket and the new Tokens are sent to the user. There's a discount sale, below a certain level of coverage (uTPDU, currently 1.6). This increases coverage, and allows to mint
(sent_btc/target_coverage)*btc_price extra DoCs, assuming the system is in the 'above coverage' state.