Program received signal SIGSEGV, Segmentation fault.
[Switching to LWP 1]
0x0000000000577c5a in balance_an_interval (i=0x4a35230) at intervals.c:444
444               new_diff = i->total_length - i->left->total_length
(gdb) bt
#0  0x0000000000577c5a in balance_an_interval (i=0x4a35230) at intervals.c:444
#1  0x0000000000577d0e in balance_an_interval (i=<optimized out>) at intervals.c:449
#2  0x0000000000577ed2 in balance_intervals_internal (tree=0x4a35188) at intervals.c:507
#3  0x0000000000577ed2 in balance_intervals_internal (tree=0x4a35668) at intervals.c:507
#4  0x0000000000577ed2 in balance_intervals_internal (tree=0x5d4ded8) at intervals.c:507
#5  0x0000000000577ed2 in balance_intervals_internal (tree=0x88ad310) at intervals.c:507
#6  0x0000000000577ed2 in balance_intervals_internal (tree=0x5af7d88) at intervals.c:507
#7  0x0000000000577ed2 in balance_intervals_internal (tree=0x7d4da68) at intervals.c:507
#8  0x0000000000577ed2 in balance_intervals_internal (tree=0x666e748) at intervals.c:507
#9  0x0000000000577ed2 in balance_intervals_internal (tree=0x49790a8) at intervals.c:507
#10 0x000000000051f318 in gc_sweep () at alloc.c:6425
#11 Fgarbage_collect () at alloc.c:5367
#12 0x0000000000533d43 in maybe_gc () at lisp.h:4320
#13 Ffuncall (nargs=<optimized out>, args=0x7f7ffffe7630) at eval.c:2741