$MUBARAK The car wouldn’t start. He swallowed his anger, reached out, and gently smoothed his hand over the control panel, where the text "Transaction failed" still blazed in red. Once again, he pressed the start button, and once again the familiar message appeared. In his wallet there were only two coins left—enough to get through the day, but not enough to buy a transaction confirmation signature. He muttered to himself, recalling that stormy night, $PTB $XRP