><code>exec_instr astate proc_data node idx instr</code> should usually return <code>astate'</code> such that <code>{astate} instr {astate'}</code> is a valid Hoare triple. In other words, <code>exec_instr</code> defines how executing an instruction from a given abstract state changes that state into a new one. This is usually called the <i>transfer function</i> in Abstract Interpretation terms. <code>node</code> is the node containing the current instruction and <code>idx</code> is the index of the instruc