The European Union and Britain held their first full session on Brexit proceedings on Monday, with both sides bent on seeking a quick breakthrough on unraveling ties that have bound them for decades.

UK Secretary of State David Davis said at the start of the four-day session that “it is incredibly important we now make good progress.”

The talks this week are set to center on the rights of citizens in each other’s nations post-Brexit, the bill Britain has to pay to meet existing commitments, the border issue in Ireland and the pre-eminence of the EU’s Court of Justice.