### Database Schema:
CREATE TABLE cites (
	cited_paper_id	TEXT	NOT NULL	PRIMARY KEY,
	citing_paper_id	TEXT	NOT NULL	PRIMARY KEY
);

CREATE TABLE content (
	paper_id	TEXT	NOT NULL	PRIMARY KEY,
	word_cited_id	TEXT	NOT NULL	PRIMARY KEY,
	foreign key (paper_id) references paper (paper_id)
);

CREATE TABLE paper (
	paper_id	TEXT	NOT NULL	PRIMARY KEY,
	class_label	TEXT	NOT NULL
);

### User's Query:
In the papers classified as ML, how many cited butz01algorithmic?

### Extra Knowledge:
classification refers to class_label; paper cited by refers to citing_paper_id; citing_paper_id = 'butz01algorithmic';
SELECT COUNT(T1.paper_id) FROM paper AS T1 INNER JOIN cites AS T2 ON T1.paper_id = T2.citing_paper_id WHERE T1.class_label = 'ML' AND T2.cited_paper_id = 'butz01algorithmic'