SQLite Foreign Key

CREATE TABLE parent(a PRIMARY KEY, b UNIQUE, c, d, e, f);
CREATE UNIQUE INDEX i1 ON parent(c, d);
CREATE INDEX i2 ON parent(e);
CREATE UNIQUE INDEX i3 ON parent(f COLLATE nocase);

CREATE TABLE child1(f, g REFERENCES parent(a));
-- Ok
CREATE TABLE child2(h, i REFERENCES parent(b));
-- Ok
CREATE TABLE child3(j, k, FOREIGN KEY(j, k) REFERENCES parent(c, d));
-- Ok
CREATE TABLE child4(l, m REFERENCES parent(e));
-- Error!
CREATE TABLE child5(n, o REFERENCES parent(f));
-- Error!
CREATE TABLE child6(p, q, FOREIGN KEY(p, q) REFERENCES parent(b, c));
-- Error!
CREATE TABLE child7(r REFERENCES parent(c));
-- Error!