func (op Op) Txn() ([]Cmp, []Op, []Op) {
	return op.cmps, op.thenOps, op.elseOps
}
func (op Op) Txn() ([]Cmp, []Op, []Op) {
	return op.cmps, op.thenOps, op.elseOps
}
// Txn returns the comparison(if) operations, "then" operations, and "else" operations.