When you start a new top-level, it prompts you to enter a Prolog query
by displaying the query prompt, which is usually ‘?- ’.
You post your query by typing it at the prompt, and pressing
RET (comint-send-input) to send it. If the query
succeeds with a choicepoint, the top-level lets you to perform one of
several actions by typing a single character, such as ; to get
the next answer. Sweep Top-level mode detects that the top-level
expects a single character input, and sends the character you type to
the top-level immediately. After the top-level is done with answering
your query, it prompts you again to post a new one.
The Sweep top-level provides input completion at the query prompt, which works similarly to the in-buffer completion you get in Sweep Prolog mode buffers (see Code Completion). Namely, to complete a partial predicate name or other input in the top-level prompt, type C-M-i (or M-TAB).