B_AT_HIST
ba = ba_new(bg_get(hname), B_AT_HIST);
case B_AT_HIST:
ba->ba_type == B_AT_HIST);
case B_AT_HIST:
if (ba->ba_type != B_AT_MAP && ba->ba_type != B_AT_HIST)
assert(bhist->ba_type == B_AT_HIST);