EQN_PILE
if (cur->type == EQN_PILE)
(parent->type == EQN_PILE ||
parent->type = EQN_PILE;
if (EQN_PILE == bp->type) {
bp->parent && bp->parent->type == EQN_PILE) {
bp->type == EQN_PILE &&
(bp->type == EQN_PILE && (bp->prev || bp->next)) ||
bp->first->type != EQN_PILE &&
case EQN_PILE: