b line condition

                 Set a breakpoint.  If line is  omitted,  sets  a
                 breakpoint  on the line that is about to be exe-
                 cuted.  If  a  condition  is  specified,  it  is
                 evaluated each time the statement is reached and
                 a breakpoint is taken only if the  condition  is
                 true.  Breakpoints may only be set on lines that
                 begin an executable statement.