You can create and use any number of top-levels at the same time, each
top-level with its own buffer. If a top-level buffer already exists,
sweeprolog-top-level simply opens it by default. To create
another one or more top-level buffers, run sweeprolog-top-level
with a prefix argument (C-u M-x sweeprolog-top-level RET)
to choose a different buffer name. Alternatively, run the command
C-x x u (rename-uniquely) in the buffer called
*sweeprolog-top-level* and then do M-x
sweeprolog-top-level RET again. This changes the name of the
original top-level buffer to something like
*sweeprolog-top-level*<2> and allows the new top-level to claim
the buffer name *sweeprolog-top-level*.