The solution to this problem took on many forms. One was the addition of a fin known as a "wing fence" on the upper surface of the wing to redirect the flow to the rear ; the MiG-15 was one example of an aircraft fitted with wing fences. Another closely related design was addition of a dogtooth notch to the leading edge, as present on the Avro Arrow interceptor. Other designs took a more radical approach, including the Republic XF-91 Thunderceptor's wing that grew wider towards the tip to provide more lift at the tip. The Handley Page Victor was equipped with a crescent wing, featuring substantial sweep-back near the wing root where the wing was thickest, and progressively reducing sweep along the span as the wing thickness reduced towards the tip.