sets a breakpoint at the beginning of the specified procedure or
at the given line.
Note: Line number 1 is the first line of a library (for
procedures from libraries), resp. the line with the {.
A line number of -1 removes all breakpoint from that procedure.
Example:
breakpoint(groebner);
→ breakpoint 1, at line 163 in groebner
breakpoint(groebner, 176);
→ breakpoint 2, at line 176 in groebner
breakpoint(groebner, -1);
→ breakpoints in groebner deleted(0x6)