Ref:
Question: Consider any two polygons P1 and P2 with equal area and equal perimeter. Is it always possible to dissect P1 to P2 in such a way that the every point on the boundary of P2 was also a boundary point on P1? If the answer is "yes" (likely), can some bound be derived on the number of intermediate pieces if the number of sides of P1 and P2 are n1 and n2 respectively? Will convexity have any bearing on the result?
Note: an inside out dissection of P1 to P2 seems a less constrained problem. Not sure about a totally inside out dissection.