collect(c)
		}
	}
}

// genConcat2 generates the cross product of the strings of g1 concatenated
// with those of g2.
func genConcat2(g1, g2 generator) generator {
	return func(collect func(string)) {
		g1(func(s1 string) {
			g2(func(s2 string) {
				collect(s1 + s2)
			})
		})
	}
}

// genConcat generalizes genConcat2 to any number of generators.